diff --git a/mythril/analysis/modules/base.py b/mythril/analysis/modules/base.py
index 072f74e9..d7075109 100644
--- a/mythril/analysis/modules/base.py
+++ b/mythril/analysis/modules/base.py
@@ -3,6 +3,7 @@ modules."""
 
 import logging
 from typing import List
+from mythril.analysis.report import Issue
 
 log = logging.getLogger(__name__)
 
@@ -21,7 +22,7 @@ class DetectionModule:
         entrypoint: str = "post",
         pre_hooks: List[str] = None,
         post_hooks: List[str] = None,
-    ):
+    ) -> None:
         self.name = name
         self.swc_id = swc_id
         self.pre_hooks = pre_hooks if pre_hooks else []
@@ -33,7 +34,7 @@ class DetectionModule:
                 self.name,
             )
         self.entrypoint = entrypoint
-        self._issues = []
+        self._issues = []  # type: List[Issue]
 
     @property
     def issues(self):
diff --git a/mythril/analysis/modules/delegatecall.py b/mythril/analysis/modules/delegatecall.py
index 596f8ce5..9ebfcd17 100644
--- a/mythril/analysis/modules/delegatecall.py
+++ b/mythril/analysis/modules/delegatecall.py
@@ -17,7 +17,7 @@ log = logging.getLogger(__name__)
 class DelegateCallModule(DetectionModule):
     """This module detects calldata being forwarded using DELEGATECALL."""
 
-    def __init__(self):
+    def __init__(self) -> None:
         """"""
         super().__init__(
             name="DELEGATECALL Usage in Fallback Function",
@@ -46,7 +46,7 @@ def _analyze_states(state: GlobalState) -> List[Issue]:
     call = get_call_from_state(state)
     if call is None:
         return []
-    issues = []
+    issues = []  # type: List[Issue]
 
     if call.type is not "DELEGATECALL":
         return []
diff --git a/mythril/analysis/modules/dependence_on_predictable_vars.py b/mythril/analysis/modules/dependence_on_predictable_vars.py
index 632672b8..1450f93a 100644
--- a/mythril/analysis/modules/dependence_on_predictable_vars.py
+++ b/mythril/analysis/modules/dependence_on_predictable_vars.py
@@ -19,7 +19,7 @@ class PredictableDependenceModule(DetectionModule):
     """This module detects whether Ether is sent using predictable
     parameters."""
 
-    def __init__(self):
+    def __init__(self) -> None:
         """"""
         super().__init__(
             name="Dependence of Predictable Variables",
@@ -118,9 +118,9 @@ def _analyze_states(state: GlobalState) -> list:
                 m = re.search(r"blockhash\w+(\s-\s(\d+))*", str(constraint))
                 if m and solve(call):
 
-                    found = m.group(1)
+                    found_item = m.group(1)
 
-                    if found:  # block.blockhash(block.number - N)
+                    if found_item:  # block.blockhash(block.number - N)
                         description = (
                             "The predictable expression 'block.blockhash(block.number - "
                             + m.group(2)
diff --git a/mythril/analysis/modules/integer.py b/mythril/analysis/modules/integer.py
index c11b40ed..6cbfd5ac 100644
--- a/mythril/analysis/modules/integer.py
+++ b/mythril/analysis/modules/integer.py
@@ -2,7 +2,7 @@
 underflows."""
 
 import json
-
+from typing import Dict
 from mythril.analysis import solver
 from mythril.analysis.report import Issue
 from mythril.analysis.swc_data import INTEGER_OVERFLOW_AND_UNDERFLOW
@@ -27,7 +27,9 @@ log = logging.getLogger(__name__)
 
 
 class OverUnderflowAnnotation:
-    def __init__(self, overflowing_state: GlobalState, operator: str, constraint):
+    def __init__(
+        self, overflowing_state: GlobalState, operator: str, constraint
+    ) -> None:
         self.overflowing_state = overflowing_state
         self.operator = operator
         self.constraint = constraint
@@ -36,7 +38,7 @@ class OverUnderflowAnnotation:
 class IntegerOverflowUnderflowModule(DetectionModule):
     """This module searches for integer over- and underflows."""
 
-    def __init__(self):
+    def __init__(self) -> None:
         """"""
         super().__init__(
             name="Integer Overflow and Underflow",
@@ -49,8 +51,8 @@ class IntegerOverflowUnderflowModule(DetectionModule):
             entrypoint="callback",
             pre_hooks=["ADD", "MUL", "SUB", "SSTORE", "JUMPI"],
         )
-        self._overflow_cache = {}
-        self._underflow_cache = {}
+        self._overflow_cache = {}  # type: Dict[int, bool]
+        self._underflow_cache = {}  # type: Dict[int, bool]
 
     def reset_module(self):
         """
diff --git a/mythril/analysis/modules/multiple_sends.py b/mythril/analysis/modules/multiple_sends.py
index 04a74bce..fbe0c03b 100644
--- a/mythril/analysis/modules/multiple_sends.py
+++ b/mythril/analysis/modules/multiple_sends.py
@@ -1,7 +1,9 @@
 """This module contains the detection code to find multiple sends occurring in
 a single transaction."""
 from copy import copy
+from typing import cast, List, Optional
 
+from mythril.analysis.ops import Call
 from mythril.analysis.report import Issue
 from mythril.analysis.swc_data import MULTIPLE_SENDS
 from mythril.analysis.modules.base import DetectionModule
@@ -14,8 +16,8 @@ log = logging.getLogger(__name__)
 
 
 class MultipleSendsAnnotation(StateAnnotation):
-    def __init__(self):
-        self.calls = []
+    def __init__(self) -> None:
+        self.calls = []  # type: List[Optional[Call]]
 
     def __copy__(self):
         result = MultipleSendsAnnotation()
@@ -56,11 +58,17 @@ def _analyze_state(state: GlobalState):
     node = state.node
     instruction = state.get_current_instruction()
 
-    annotations = [a for a in state.get_annotations(MultipleSendsAnnotation)]
+    annotations = cast(
+        List[MultipleSendsAnnotation],
+        [a for a in state.get_annotations(MultipleSendsAnnotation)],
+    )
     if len(annotations) == 0:
         log.debug("Creating annotation for state")
         state.annotate(MultipleSendsAnnotation())
-        annotations = [a for a in state.get_annotations(MultipleSendsAnnotation)]
+        annotations = cast(
+            List[MultipleSendsAnnotation],
+            [a for a in state.get_annotations(MultipleSendsAnnotation)],
+        )
 
     calls = annotations[0].calls
 
diff --git a/mythril/analysis/modules/unchecked_retval.py b/mythril/analysis/modules/unchecked_retval.py
index 70d7f0fd..5beb0fda 100644
--- a/mythril/analysis/modules/unchecked_retval.py
+++ b/mythril/analysis/modules/unchecked_retval.py
@@ -1,12 +1,15 @@
 """This module contains detection code to find occurrences of calls whose
 return value remains unchecked."""
 from copy import copy
+from typing import cast, List, Union, Mapping
 
 from mythril.analysis import solver
 from mythril.analysis.report import Issue
 from mythril.analysis.swc_data import UNCHECKED_RET_VAL
 from mythril.analysis.modules.base import DetectionModule
 from mythril.exceptions import UnsatError
+from mythril.laser.smt.bitvec import BitVec
+
 from mythril.laser.ethereum.state.annotation import StateAnnotation
 from mythril.laser.ethereum.state.global_state import GlobalState
 
@@ -16,8 +19,8 @@ log = logging.getLogger(__name__)
 
 
 class UncheckedRetvalAnnotation(StateAnnotation):
-    def __init__(self):
-        self.retvals = []
+    def __init__(self) -> None:
+        self.retvals = []  # type: List[Mapping[str, Union[int, BitVec]]]
 
     def __copy__(self):
         result = UncheckedRetvalAnnotation()
@@ -60,10 +63,16 @@ def _analyze_state(state: GlobalState) -> list:
     instruction = state.get_current_instruction()
     node = state.node
 
-    annotations = [a for a in state.get_annotations(UncheckedRetvalAnnotation)]
+    annotations = cast(
+        List[UncheckedRetvalAnnotation],
+        [a for a in state.get_annotations(UncheckedRetvalAnnotation)],
+    )
     if len(annotations) == 0:
         state.annotate(UncheckedRetvalAnnotation())
-        annotations = [a for a in state.get_annotations(UncheckedRetvalAnnotation)]
+        annotations = cast(
+            List[UncheckedRetvalAnnotation],
+            [a for a in state.get_annotations(UncheckedRetvalAnnotation)],
+        )
 
     retvals = annotations[0].retvals
 
@@ -103,7 +112,13 @@ def _analyze_state(state: GlobalState) -> list:
             "opcode"
         ] in ["CALL", "DELEGATECALL", "STATICCALL", "CALLCODE"]
         retval = state.mstate.stack[-1]
-        retvals.append({"address": state.instruction["address"] - 1, "retval": retval})
+        # Use Typed Dict after release of mypy 0.670 and remove type ignore
+        retvals.append(
+            {  # type: ignore
+                "address": state.instruction["address"] - 1,
+                "retval": retval,
+            }
+        )
 
     return []
 
diff --git a/mythril/disassembler/asm.py b/mythril/disassembler/asm.py
index 2c9c7907..cbbe1881 100644
--- a/mythril/disassembler/asm.py
+++ b/mythril/disassembler/asm.py
@@ -90,7 +90,7 @@ def is_sequence_match(pattern: list, instruction_list: list, index: int) -> bool
     return True
 
 
-def disassemble(bytecode: str) -> list:
+def disassemble(bytecode: bytes) -> list:
     """Disassembles evm bytecode and returns a list of instructions.
 
     :param bytecode:
diff --git a/mythril/disassembler/disassembly.py b/mythril/disassembler/disassembly.py
index 0d4828fc..0cc1c8aa 100644
--- a/mythril/disassembler/disassembly.py
+++ b/mythril/disassembler/disassembly.py
@@ -3,6 +3,8 @@ from mythril.ethereum import util
 from mythril.disassembler import asm
 from mythril.support.signatures import SignatureDB
 
+from typing import Dict, List, Tuple
+
 
 class Disassembly(object):
     """Disassembly class.
@@ -14,7 +16,7 @@ class Disassembly(object):
     - function entry point to function name mapping
     """
 
-    def __init__(self, code: str, enable_online_lookup: bool = False):
+    def __init__(self, code: str, enable_online_lookup: bool = False) -> None:
         """
 
         :param code:
@@ -23,9 +25,9 @@ class Disassembly(object):
         self.bytecode = code
         self.instruction_list = asm.disassemble(util.safe_decode(code))
 
-        self.func_hashes = []
-        self.function_name_to_address = {}
-        self.address_to_function_name = {}
+        self.func_hashes = []  # type: List[str]
+        self.function_name_to_address = {}  # type: Dict[str, int]
+        self.address_to_function_name = {}  # type: Dict[int, str]
 
         # open from default locations
         # control if you want to have online signature hash lookups
@@ -41,7 +43,6 @@ class Disassembly(object):
                 index, self.instruction_list, signatures
             )
             self.func_hashes.append(function_hash)
-
             if jump_target is not None and function_name is not None:
                 self.function_name_to_address[function_name] = jump_target
                 self.address_to_function_name[jump_target] = function_name
@@ -56,7 +57,7 @@ class Disassembly(object):
 
 def get_function_info(
     index: int, instruction_list: list, signature_database: SignatureDB
-) -> (str, int, str):
+) -> Tuple[str, int, str]:
     """Finds the function information for a call table entry Solidity uses the
     first 4 bytes of the calldata to indicate which function the message call
     should execute The generated code that directs execution to the correct
diff --git a/mythril/laser/ethereum/call.py b/mythril/laser/ethereum/call.py
index 7ee0af34..27df993e 100644
--- a/mythril/laser/ethereum/call.py
+++ b/mythril/laser/ethereum/call.py
@@ -3,9 +3,9 @@ instructions.py to get the necessary elements from the stack and determine the
 parameters for the new global state."""
 
 import logging
-from typing import Union, List
+from typing import Union, List, cast, Callable
 from z3 import Z3Exception
-
+from mythril.laser.smt import BitVec
 from mythril.laser.ethereum import natives
 from mythril.laser.ethereum.gas import OPCODE_GAS
 from mythril.laser.smt import simplify, Expression, symbol_factory
@@ -155,8 +155,8 @@ def get_callee_account(
 
 def get_call_data(
     global_state: GlobalState,
-    memory_start: Union[int, Expression],
-    memory_size: Union[int, Expression],
+    memory_start: Union[int, BitVec],
+    memory_size: Union[int, BitVec],
 ):
     """Gets call_data from the global_state.
 
@@ -168,22 +168,28 @@ def get_call_data(
     state = global_state.mstate
     transaction_id = "{}_internalcall".format(global_state.current_transaction.id)
 
-    memory_start = (
-        symbol_factory.BitVecVal(memory_start, 256)
-        if isinstance(memory_start, int)
-        else memory_start
+    memory_start = cast(
+        BitVec,
+        (
+            symbol_factory.BitVecVal(memory_start, 256)
+            if isinstance(memory_start, int)
+            else memory_start
+        ),
     )
-    memory_size = (
-        symbol_factory.BitVecVal(memory_size, 256)
-        if isinstance(memory_size, int)
-        else memory_size
+    memory_size = cast(
+        BitVec,
+        (
+            symbol_factory.BitVecVal(memory_size, 256)
+            if isinstance(memory_size, int)
+            else memory_size
+        ),
     )
 
     uses_entire_calldata = simplify(
         memory_size - global_state.environment.calldata.calldatasize == 0
     )
 
-    if uses_entire_calldata == True:
+    if uses_entire_calldata is True:
         return global_state.environment.calldata
 
     try:
@@ -218,7 +224,7 @@ def native_call(
 
     contract_list = ["ecrecover", "sha256", "ripemd160", "identity"]
     call_address_int = int(callee_address, 16)
-    native_gas_min, native_gas_max = OPCODE_GAS["NATIVE_COST"](
+    native_gas_min, native_gas_max = cast(Callable, OPCODE_GAS["NATIVE_COST"])(
         global_state.mstate.calculate_extension_size(mem_out_start, mem_out_sz),
         contract_list[call_address_int - 1],
     )
diff --git a/mythril/laser/ethereum/cfg.py b/mythril/laser/ethereum/cfg.py
index 056692e5..0578c602 100644
--- a/mythril/laser/ethereum/cfg.py
+++ b/mythril/laser/ethereum/cfg.py
@@ -1,9 +1,12 @@
 """This module."""
 from enum import Enum
-from typing import Dict
+from typing import Dict, List, TYPE_CHECKING
 
 from flags import Flags
 
+if TYPE_CHECKING:
+    from mythril.laser.ethereum.state.global_state import GlobalState
+
 gbl_next_uid = 0  # node counter
 
 
@@ -20,6 +23,9 @@ class JumpType(Enum):
 class NodeFlags(Flags):
     """A collection of flags to denote the type a call graph node can have."""
 
+    def __or__(self, other) -> "NodeFlags":
+        return super().__or__(other)
+
     FUNC_ENTRY = 1
     CALL_RETURN = 2
 
@@ -33,7 +39,7 @@ class Node:
         start_addr=0,
         constraints=None,
         function_name="unknown",
-    ):
+    ) -> None:
         """
 
         :param contract_name:
@@ -43,7 +49,7 @@ class Node:
         constraints = constraints if constraints else []
         self.contract_name = contract_name
         self.start_addr = start_addr
-        self.states = []
+        self.states = []  # type: List[GlobalState]
         self.constraints = constraints
         self.function_name = function_name
         self.flags = NodeFlags()
@@ -86,7 +92,7 @@ class Edge:
         node_to: int,
         edge_type=JumpType.UNCONDITIONAL,
         condition=None,
-    ):
+    ) -> None:
         """
 
         :param node_from:
diff --git a/mythril/laser/ethereum/gas.py b/mythril/laser/ethereum/gas.py
index 43c5d48b..8fae5f53 100644
--- a/mythril/laser/ethereum/gas.py
+++ b/mythril/laser/ethereum/gas.py
@@ -2,6 +2,7 @@
 table."""
 from ethereum import opcodes
 from ethereum.utils import ceil32
+from typing import Callable, Dict, Tuple, Union
 
 
 def calculate_native_gas(size: int, contract: str):
@@ -185,4 +186,4 @@ OPCODE_GAS = {
     "SUICIDE": (5000, 30000),
     "ASSERT_FAIL": (0, 0),
     "INVALID": (0, 0),
-}
+}  # type: Dict[str, Union[Tuple[int, int], Callable]]
diff --git a/mythril/laser/ethereum/instructions.py b/mythril/laser/ethereum/instructions.py
index 8ea097fe..ab0df0b3 100644
--- a/mythril/laser/ethereum/instructions.py
+++ b/mythril/laser/ethereum/instructions.py
@@ -4,7 +4,7 @@ import binascii
 import logging
 
 from copy import copy, deepcopy
-from typing import Callable, List, Union
+from typing import cast, Callable, List, Union, Tuple
 from datetime import datetime
 
 from ethereum import utils
@@ -127,7 +127,7 @@ class StateTransition(object):
         if not self.enable_gas:
             return global_state
         opcode = global_state.instruction["opcode"]
-        min_gas, max_gas = OPCODE_GAS[opcode]
+        min_gas, max_gas = cast(Tuple[int, int], OPCODE_GAS[opcode])
         global_state.mstate.min_gas_used += min_gas
         global_state.mstate.max_gas_used += max_gas
         return global_state
@@ -155,7 +155,7 @@ class Instruction:
     """Instruction class is used to mutate a state according to the current
     instruction."""
 
-    def __init__(self, op_code: str, dynamic_loader: DynLoader, iprof=None):
+    def __init__(self, op_code: str, dynamic_loader: DynLoader, iprof=None) -> None:
         """
 
         :param op_code:
@@ -358,7 +358,7 @@ class Instruction:
                         symbol_factory.BitVecVal(0, 248),
                         Extract(offset + 7, offset, op1),
                     )
-                )
+                )  # type: Union[int, Expression]
             else:
                 result = 0
         except TypeError:
@@ -717,17 +717,15 @@ class Instruction:
             log.debug("Unsupported symbolic memory offset in CALLDATACOPY")
             return [global_state]
 
-        dstart_sym = False
         try:
-            dstart = util.get_concrete_int(op1)
+            dstart = util.get_concrete_int(op1)  # type: Union[int, BitVec]
         except TypeError:
             log.debug("Unsupported symbolic calldata offset in CALLDATACOPY")
             dstart = simplify(op1)
-            dstart_sym = True
 
         size_sym = False
         try:
-            size = util.get_concrete_int(op2)
+            size = util.get_concrete_int(op2)  # type: Union[int, BitVec]
         except TypeError:
             log.debug("Unsupported symbolic size in CALLDATACOPY")
             size = simplify(op2)
@@ -746,7 +744,7 @@ class Instruction:
                 8,
             )
             return [global_state]
-
+        size = cast(int, size)
         if size > 0:
             try:
                 state.mem_extend(mstart, size)
@@ -778,7 +776,9 @@ class Instruction:
                     new_memory.append(value)
 
                     i_data = (
-                        i_data + 1 if isinstance(i_data, int) else simplify(i_data + 1)
+                        i_data + 1
+                        if isinstance(i_data, int)
+                        else simplify(cast(BitVec, i_data) + 1)
                     )
                 for i in range(len(new_memory)):
                     state.memory[i + mstart] = new_memory[i]
@@ -881,11 +881,12 @@ class Instruction:
             state.stack.append(
                 symbol_factory.BitVecSym("KECCAC_mem[" + str(op0) + "]", 256)
             )
-            state.min_gas_used += OPCODE_GAS["SHA3"][0]
-            state.max_gas_used += OPCODE_GAS["SHA3"][1]
+            gas_tuple = cast(Tuple, OPCODE_GAS["SHA3"])
+            state.min_gas_used += gas_tuple[0]
+            state.max_gas_used += gas_tuple[1]
             return [global_state]
 
-        min_gas, max_gas = OPCODE_GAS["SHA3_FUNC"](length)
+        min_gas, max_gas = cast(Callable, OPCODE_GAS["SHA3_FUNC"])(length)
         state.min_gas_used += min_gas
         state.max_gas_used += max_gas
         StateTransition.check_gas_usage_limit(global_state)
@@ -1268,7 +1269,9 @@ class Instruction:
         state.mem_extend(offset, 1)
 
         try:
-            value_to_write = util.get_concrete_int(value) ^ 0xFF
+            value_to_write = (
+                util.get_concrete_int(value) ^ 0xFF
+            )  # type: Union[int, BitVec]
         except TypeError:  # BitVec
             value_to_write = Extract(7, 0, value)
         log.debug("MSTORE8 to mem[" + str(offset) + "]: " + str(value_to_write))
@@ -1301,7 +1304,7 @@ class Instruction:
             storage_keys = global_state.environment.active_account.storage.keys()
             keccak_keys = list(filter(keccak_function_manager.is_keccak, storage_keys))
 
-            results = []
+            results = []  # type: List[GlobalState]
             constraints = []
 
             for keccak_key in keccak_keys:
@@ -1328,7 +1331,7 @@ class Instruction:
 
     @staticmethod
     def _sload_helper(
-        global_state: GlobalState, index: Union[int, Expression], constraints=None
+        global_state: GlobalState, index: Union[str, int], constraints=None
     ):
         """
 
@@ -1387,17 +1390,21 @@ class Instruction:
             storage_keys = global_state.environment.active_account.storage.keys()
             keccak_keys = filter(keccak_function_manager.is_keccak, storage_keys)
 
-            results = []
+            results = []  # type: List[GlobalState]
             new = symbol_factory.Bool(False)
 
             for keccak_key in keccak_keys:
-                key_argument = keccak_function_manager.get_argument(keccak_key)
-                index_argument = keccak_function_manager.get_argument(index)
+                key_argument = keccak_function_manager.get_argument(
+                    keccak_key
+                )  # type: Expression
+                index_argument = keccak_function_manager.get_argument(
+                    index
+                )  # type: Expression
                 condition = key_argument == index_argument
                 condition = (
                     condition
                     if type(condition) == bool
-                    else is_true(simplify(condition))
+                    else is_true(simplify(cast(Bool, condition)))
                 )
                 if condition:
                     return self._sstore_helper(
@@ -1414,7 +1421,7 @@ class Instruction:
                     key_argument == index_argument,
                 )
 
-                new = Or(new, key_argument != index_argument)
+                new = Or(new, cast(Bool, key_argument != index_argument))
 
             if len(results) > 0:
                 results += self._sstore_helper(
@@ -1482,7 +1489,7 @@ class Instruction:
 
         new_state = copy(global_state)
         # add JUMP gas cost
-        min_gas, max_gas = OPCODE_GAS["JUMP"]
+        min_gas, max_gas = cast(Tuple[int, int], OPCODE_GAS["JUMP"])
         new_state.mstate.min_gas_used += min_gas
         new_state.mstate.max_gas_used += max_gas
 
@@ -1501,7 +1508,7 @@ class Instruction:
         """
         state = global_state.mstate
         disassembly = global_state.environment.code
-        min_gas, max_gas = OPCODE_GAS["JUMPI"]
+        min_gas, max_gas = cast(Tuple[int, int], OPCODE_GAS["JUMPI"])
         states = []
 
         op0, condition = state.stack.pop(), state.stack.pop()
@@ -1910,12 +1917,12 @@ class Instruction:
         try:
             memory_out_offset = (
                 util.get_concrete_int(memory_out_offset)
-                if isinstance(memory_out_offset, ExprRef)
+                if isinstance(memory_out_offset, Expression)
                 else memory_out_offset
             )
             memory_out_size = (
                 util.get_concrete_int(memory_out_size)
-                if isinstance(memory_out_size, ExprRef)
+                if isinstance(memory_out_size, Expression)
                 else memory_out_size
             )
         except TypeError:
diff --git a/mythril/laser/ethereum/keccak.py b/mythril/laser/ethereum/keccak.py
index 9d2aefdc..47a39ed1 100644
--- a/mythril/laser/ethereum/keccak.py
+++ b/mythril/laser/ethereum/keccak.py
@@ -18,7 +18,7 @@ class KeccakFunctionManager:
         """
         return str(expression) in self.keccak_expression_mapping.keys()
 
-    def get_argument(self, expression: str) -> Expression:
+    def get_argument(self, expression: Expression) -> Expression:
         """
 
         :param expression:
diff --git a/mythril/laser/ethereum/natives.py b/mythril/laser/ethereum/natives.py
index 205e325a..ef38d8c9 100644
--- a/mythril/laser/ethereum/natives.py
+++ b/mythril/laser/ethereum/natives.py
@@ -9,7 +9,8 @@ from py_ecc.secp256k1 import N as secp256k1n
 from rlp.utils import ALL_BYTES
 
 from mythril.laser.ethereum.state.calldata import BaseCalldata, ConcreteCalldata
-from mythril.laser.ethereum.util import bytearray_to_int, sha3
+from mythril.laser.ethereum.util import bytearray_to_int
+from ethereum.utils import sha3
 from mythril.laser.smt import Concat, simplify
 
 log = logging.getLogger(__name__)
@@ -50,7 +51,7 @@ def extract32(data: bytearray, i: int) -> int:
     return bytearray_to_int(o)
 
 
-def ecrecover(data: Union[bytes, str, List[int]]) -> bytes:
+def ecrecover(data: List[int]) -> List[int]:
     """
 
     :param data:
@@ -58,54 +59,54 @@ def ecrecover(data: Union[bytes, str, List[int]]) -> bytes:
     """
     # TODO: Add type hints
     try:
-        data = bytearray(data)
-        v = extract32(data, 32)
-        r = extract32(data, 64)
-        s = extract32(data, 96)
+        byte_data = bytearray(data)
+        v = extract32(byte_data, 32)
+        r = extract32(byte_data, 64)
+        s = extract32(byte_data, 96)
     except TypeError:
         raise NativeContractException
 
-    message = b"".join([ALL_BYTES[x] for x in data[0:32]])
+    message = b"".join([ALL_BYTES[x] for x in byte_data[0:32]])
     if r >= secp256k1n or s >= secp256k1n or v < 27 or v > 28:
         return []
     try:
         pub = ecrecover_to_pub(message, v, r, s)
     except Exception as e:
-        log.debug("An error has occured while extracting public key: " + e)
+        log.debug("An error has occured while extracting public key: " + str(e))
         return []
     o = [0] * 12 + [x for x in sha3(pub)[-20:]]
-    return o
+    return list(bytearray(o))
 
 
-def sha256(data: Union[bytes, str, List[int]]) -> bytes:
+def sha256(data: List[int]) -> List[int]:
     """
 
     :param data:
     :return:
     """
     try:
-        data = bytes(data)
+        byte_data = bytes(data)
     except TypeError:
         raise NativeContractException
-    return hashlib.sha256(data).digest()
+    return list(bytearray(hashlib.sha256(byte_data).digest()))
 
 
-def ripemd160(data: Union[bytes, str, List[int]]) -> bytes:
+def ripemd160(data: List[int]) -> List[int]:
     """
 
     :param data:
     :return:
     """
     try:
-        data = bytes(data)
+        bytes_data = bytes(data)
     except TypeError:
         raise NativeContractException
-    digest = hashlib.new("ripemd160", data).digest()
+    digest = hashlib.new("ripemd160", bytes_data).digest()
     padded = 12 * [0] + list(digest)
-    return bytes(padded)
+    return list(bytearray(bytes(padded)))
 
 
-def identity(data: Union[bytes, str, List[int]]) -> bytes:
+def identity(data: List[int]) -> List[int]:
     """
 
     :param data:
@@ -117,13 +118,9 @@ def identity(data: Union[bytes, str, List[int]]) -> bytes:
     # implementation would be byte indexed for the most
     # part.
     return data
-    result = []
-    for i in range(0, len(data), 32):
-        result.append(simplify(Concat(data[i : i + 32])))
-    return result
 
 
-def native_contracts(address: int, data: BaseCalldata):
+def native_contracts(address: int, data: BaseCalldata) -> List[int]:
     """Takes integer address 1, 2, 3, 4.
 
     :param address:
@@ -133,8 +130,8 @@ def native_contracts(address: int, data: BaseCalldata):
     functions = (ecrecover, sha256, ripemd160, identity)
 
     if isinstance(data, ConcreteCalldata):
-        data = data.concrete(None)
+        concrete_data = data.concrete(None)
     else:
         raise NativeContractException()
 
-    return functions[address - 1](data)
+    return functions[address - 1](concrete_data)
diff --git a/mythril/laser/ethereum/state/account.py b/mythril/laser/ethereum/state/account.py
index 2c69dbc5..c13c3f2f 100644
--- a/mythril/laser/ethereum/state/account.py
+++ b/mythril/laser/ethereum/state/account.py
@@ -14,17 +14,17 @@ from mythril.laser.smt import symbol_factory
 class Storage:
     """Storage class represents the storage of an Account."""
 
-    def __init__(self, concrete=False, address=None, dynamic_loader=None):
+    def __init__(self, concrete=False, address=None, dynamic_loader=None) -> None:
         """Constructor for Storage.
 
         :param concrete: bool indicating whether to interpret uninitialized storage as concrete versus symbolic
         """
-        self._storage = {}
+        self._storage = {}  # type: Dict[Union[int, str], Any]
         self.concrete = concrete
         self.dynld = dynamic_loader
         self.address = address
 
-    def __getitem__(self, item: Union[int, slice]) -> Any:
+    def __getitem__(self, item: Union[str, int]) -> Any:
         try:
             return self._storage[item]
         except KeyError:
@@ -51,7 +51,7 @@ class Storage:
         self._storage[item] = symbol_factory.BitVecVal(0, 256)
         return self._storage[item]
 
-    def __setitem__(self, key: str, value: ExprRef) -> None:
+    def __setitem__(self, key: Union[int, str], value: Any) -> None:
         self._storage[key] = value
 
     def keys(self) -> KeysView:
@@ -73,7 +73,7 @@ class Account:
         balance=None,
         concrete_storage=False,
         dynamic_loader=None,
-    ):
+    ) -> None:
         """Constructor for account.
 
         :param address: Address of the account
diff --git a/mythril/laser/ethereum/state/calldata.py b/mythril/laser/ethereum/state/calldata.py
index b2ea15a0..a8ebfa2b 100644
--- a/mythril/laser/ethereum/state/calldata.py
+++ b/mythril/laser/ethereum/state/calldata.py
@@ -1,7 +1,6 @@
 """This module declares classes to represent call data."""
-from typing import Union, Any
+from typing import cast, Union, Tuple, List
 
-from mythril.laser.smt import K, Array, If, simplify, Concat, Expression, BitVec
 
 from enum import Enum
 from typing import Any, Union
@@ -13,6 +12,7 @@ from mythril.laser.ethereum.util import get_concrete_int
 from mythril.laser.smt import (
     Array,
     BitVec,
+    Bool,
     Concat,
     Expression,
     If,
@@ -26,7 +26,7 @@ class BaseCalldata:
     """Base calldata class This represents the calldata provided when sending a
     transaction to a contract."""
 
-    def __init__(self, tx_id):
+    def __init__(self, tx_id: str) -> None:
         """
 
         :param tx_id:
@@ -34,7 +34,7 @@ class BaseCalldata:
         self.tx_id = tx_id
 
     @property
-    def calldatasize(self) -> Expression:
+    def calldatasize(self) -> BitVec:
         """
 
         :return: Calldata size for this calldata object
@@ -53,7 +53,7 @@ class BaseCalldata:
         parts = self[offset : offset + 32]
         return simplify(Concat(parts))
 
-    def __getitem__(self, item: Union[int, slice]) -> Any:
+    def __getitem__(self, item: Union[int, slice, BitVec]) -> Any:
         """
 
         :param item:
@@ -88,7 +88,7 @@ class BaseCalldata:
 
         raise ValueError
 
-    def _load(self, item: Union[int, Expression]) -> Any:
+    def _load(self, item: Union[int, BitVec]) -> Any:
         """
 
         :param item:
@@ -96,7 +96,7 @@ class BaseCalldata:
         raise NotImplementedError()
 
     @property
-    def size(self) -> Union[Expression, int]:
+    def size(self) -> Union[BitVec, int]:
         """Returns the exact size of this calldata, this is not normalized.
 
         :return: unnormalized call data size
@@ -114,7 +114,7 @@ class BaseCalldata:
 class ConcreteCalldata(BaseCalldata):
     """A concrete call data representation."""
 
-    def __init__(self, tx_id: int, calldata: list):
+    def __init__(self, tx_id: str, calldata: list) -> None:
         """Initializes the ConcreteCalldata object.
 
         :param tx_id: Id of the transaction that the calldata is for.
@@ -132,7 +132,7 @@ class ConcreteCalldata(BaseCalldata):
 
         super().__init__(tx_id)
 
-    def _load(self, item: Union[int, Expression]) -> BitVec:
+    def _load(self, item: Union[int, BitVec]) -> BitVec:
         """
 
         :param item:
@@ -161,7 +161,7 @@ class ConcreteCalldata(BaseCalldata):
 class BasicConcreteCalldata(BaseCalldata):
     """A base class to represent concrete call data."""
 
-    def __init__(self, tx_id: int, calldata: list):
+    def __init__(self, tx_id: str, calldata: list) -> None:
         """Initializes the ConcreteCalldata object, that doesn't use z3 arrays.
 
         :param tx_id: Id of the transaction that the calldata is for.
@@ -184,7 +184,7 @@ class BasicConcreteCalldata(BaseCalldata):
 
         value = symbol_factory.BitVecVal(0x0, 8)
         for i in range(self.size):
-            value = If(item == i, self._calldata[i], value)
+            value = If(cast(Union[BitVec, Bool], item) == i, self._calldata[i], value)
         return value
 
     def concrete(self, model: Model) -> list:
@@ -207,7 +207,7 @@ class BasicConcreteCalldata(BaseCalldata):
 class SymbolicCalldata(BaseCalldata):
     """A class for representing symbolic call data."""
 
-    def __init__(self, tx_id: int):
+    def __init__(self, tx_id: str) -> None:
         """Initializes the SymbolicCalldata object.
 
         :param tx_id: Id of the transaction that the calldata is for.
@@ -216,7 +216,7 @@ class SymbolicCalldata(BaseCalldata):
         self._calldata = Array("{}_calldata".format(tx_id), 256, 8)
         super().__init__(tx_id)
 
-    def _load(self, item: Union[int, Expression]) -> Any:
+    def _load(self, item: Union[int, BitVec]) -> Any:
         """
 
         :param item:
@@ -226,7 +226,7 @@ class SymbolicCalldata(BaseCalldata):
         return simplify(
             If(
                 item < self._size,
-                simplify(self._calldata[item]),
+                simplify(self._calldata[cast(BitVec, item)]),
                 symbol_factory.BitVecVal(0, 8),
             )
         )
@@ -247,7 +247,7 @@ class SymbolicCalldata(BaseCalldata):
         return result
 
     @property
-    def size(self) -> Expression:
+    def size(self) -> BitVec:
         """
 
         :return:
@@ -258,29 +258,34 @@ class SymbolicCalldata(BaseCalldata):
 class BasicSymbolicCalldata(BaseCalldata):
     """A basic class representing symbolic call data."""
 
-    def __init__(self, tx_id: int):
+    def __init__(self, tx_id: str) -> None:
         """Initializes the SymbolicCalldata object.
 
         :param tx_id: Id of the transaction that the calldata is for.
         """
-        self._reads = []
-        self._size = BitVec(str(tx_id) + "_calldatasize", 256)
+        self._reads = []  # type: List[Tuple[Union[int, BitVec], BitVec]]
+        self._size = symbol_factory.BitVecSym(str(tx_id) + "_calldatasize", 256)
         super().__init__(tx_id)
 
-    def _load(self, item: Union[int, Expression], clean=False) -> Any:
-        x = symbol_factory.BitVecVal(item, 256) if isinstance(item, int) else item
+    def _load(self, item: Union[int, BitVec], clean=False) -> Any:
+        expr_item = (
+            symbol_factory.BitVecVal(item, 256) if isinstance(item, int) else item
+        )  # type: BitVec
 
         symbolic_base_value = If(
-            x >= self._size,
+            expr_item >= self._size,
             symbol_factory.BitVecVal(0, 8),
-            BitVec("{}_calldata_{}".format(self.tx_id, str(item)), 8),
+            BitVec(
+                symbol_factory.BitVecSym(
+                    "{}_calldata_{}".format(self.tx_id, str(item)), 8
+                )
+            ),
         )
         return_value = symbolic_base_value
         for r_index, r_value in self._reads:
-            return_value = If(r_index == item, r_value, return_value)
-
+            return_value = If(r_index == expr_item, r_value, return_value)
         if not clean:
-            self._reads.append((item, symbolic_base_value))
+            self._reads.append((expr_item, symbolic_base_value))
         return simplify(return_value)
 
     def concrete(self, model: Model) -> list:
@@ -299,7 +304,7 @@ class BasicSymbolicCalldata(BaseCalldata):
         return result
 
     @property
-    def size(self) -> Expression:
+    def size(self) -> BitVec:
         """
 
         :return:
diff --git a/mythril/laser/ethereum/state/environment.py b/mythril/laser/ethereum/state/environment.py
index 6fb018ab..69830007 100644
--- a/mythril/laser/ethereum/state/environment.py
+++ b/mythril/laser/ethereum/state/environment.py
@@ -22,7 +22,7 @@ class Environment:
         callvalue: ExprRef,
         origin: ExprRef,
         code=None,
-    ):
+    ) -> None:
         """
 
         :param active_account:
diff --git a/mythril/laser/ethereum/state/global_state.py b/mythril/laser/ethereum/state/global_state.py
index 8facc663..aa931606 100644
--- a/mythril/laser/ethereum/state/global_state.py
+++ b/mythril/laser/ethereum/state/global_state.py
@@ -1,5 +1,5 @@
 """This module contains a representation of the global execution state."""
-from typing import Dict, Union, List, Iterable
+from typing import Dict, Union, List, Iterable, TYPE_CHECKING
 
 from copy import copy, deepcopy
 from z3 import BitVec
@@ -10,6 +10,13 @@ from mythril.laser.ethereum.state.environment import Environment
 from mythril.laser.ethereum.state.machine_state import MachineState
 from mythril.laser.ethereum.state.annotation import StateAnnotation
 
+if TYPE_CHECKING:
+    from mythril.laser.ethereum.state.world_state import WorldState
+    from mythril.laser.ethereum.transaction.transaction_models import (
+        MessageCallTransaction,
+        ContractCreationTransaction,
+    )
+
 
 class GlobalState:
     """GlobalState represents the current globalstate."""
@@ -23,7 +30,7 @@ class GlobalState:
         transaction_stack=None,
         last_return_data=None,
         annotations=None,
-    ):
+    ) -> None:
         """Constructor for GlobalState.
 
         :param world_state:
diff --git a/mythril/laser/ethereum/state/machine_state.py b/mythril/laser/ethereum/state/machine_state.py
index 45e824db..0ee781ae 100644
--- a/mythril/laser/ethereum/state/machine_state.py
+++ b/mythril/laser/ethereum/state/machine_state.py
@@ -1,9 +1,9 @@
 """This module contains a representation of the EVM's machine state and its
 stack."""
 from copy import copy
-from typing import Union, Any, List, Dict
+from typing import cast, Sized, Union, Any, List, Dict, Optional
 
-from z3 import BitVec
+from mythril.laser.smt import BitVec, Expression
 
 from ethereum import opcodes, utils
 from mythril.laser.ethereum.evm_exceptions import (
@@ -20,16 +20,14 @@ class MachineStack(list):
 
     STACK_LIMIT = 1024
 
-    def __init__(self, default_list=None):
+    def __init__(self, default_list=None) -> None:
         """
 
         :param default_list:
         """
-        if default_list is None:
-            default_list = []
-        super(MachineStack, self).__init__(default_list)
+        super(MachineStack, self).__init__(default_list or [])
 
-    def append(self, element: BitVec) -> None:
+    def append(self, element: Union[int, Expression]) -> None:
         """
         :param element: element to be appended to the list
         :function: appends the element to list if the size is less than STACK_LIMIT, else throws an error
@@ -41,7 +39,7 @@ class MachineStack(list):
             )
         super(MachineStack, self).append(element)
 
-    def pop(self, index=-1) -> BitVec:
+    def pop(self, index=-1) -> Union[int, Expression]:
         """
         :param index:index to be popped, same as the list() class.
         :returns popped value
@@ -90,12 +88,12 @@ class MachineState:
         gas_limit: int,
         pc=0,
         stack=None,
-        memory=None,
+        memory: Optional[Memory] = None,
         constraints=None,
         depth=0,
         max_gas_used=0,
         min_gas_used=0,
-    ):
+    ) -> None:
         """Constructor for machineState.
 
         :param gas_limit:
@@ -164,7 +162,7 @@ class MachineState:
             self.check_gas()
             self.memory.extend(m_extend)
 
-    def memory_write(self, offset: int, data: List[int]) -> None:
+    def memory_write(self, offset: int, data: List[Union[int, BitVec]]) -> None:
         """Writes data to memory starting at offset.
 
         :param offset:
@@ -217,7 +215,7 @@ class MachineState:
 
         :return:
         """
-        return len(self.memory)
+        return len(cast(Sized, self.memory))
 
     @property
     def as_dict(self) -> Dict:
diff --git a/mythril/laser/ethereum/state/memory.py b/mythril/laser/ethereum/state/memory.py
index 64be50f3..4fac4120 100644
--- a/mythril/laser/ethereum/state/memory.py
+++ b/mythril/laser/ethereum/state/memory.py
@@ -1,5 +1,5 @@
 """This module contains a representation of a smart contract's memory."""
-from typing import Union
+from typing import cast, List, Union, overload
 
 from z3 import Z3Exception
 
@@ -20,7 +20,7 @@ class Memory:
 
     def __init__(self):
         """"""
-        self._memory = []
+        self._memory = []  # type: List[Union[int, BitVec]]
 
     def __len__(self):
         """
@@ -50,12 +50,14 @@ class Memory:
                 ),
                 256,
             )
-        except:
+        except TypeError:
             result = simplify(
                 Concat(
                     [
                         b if isinstance(b, BitVec) else symbol_factory.BitVecVal(b, 8)
-                        for b in self[index : index + 32]
+                        for b in cast(
+                            List[Union[int, BitVec]], self[index : index + 32]
+                        )
                     ]
                 )
             )
@@ -79,8 +81,9 @@ class Memory:
             else:
                 _bytes = util.concrete_int_to_bytes(value)
             assert len(_bytes) == 32
-            self[index : index + 32] = _bytes
+            self[index : index + 32] = list(bytearray(_bytes))
         except (Z3Exception, AttributeError):  # BitVector or BoolRef
+            value = cast(Union[BitVec, Bool], value)
             if isinstance(value, Bool):
                 value_to_write = If(
                     value,
@@ -94,7 +97,17 @@ class Memory:
             for i in range(0, value_to_write.size(), 8):
                 self[index + 31 - (i // 8)] = Extract(i + 7, i, value_to_write)
 
-    def __getitem__(self, item: Union[int, slice]) -> Union[BitVec, int, list]:
+    @overload
+    def __getitem__(self, item: int) -> Union[int, BitVec]:
+        ...
+
+    @overload
+    def __getitem__(self, item: slice) -> List[Union[int, BitVec]]:
+        ...
+
+    def __getitem__(
+        self, item: Union[int, slice]
+    ) -> Union[BitVec, int, List[Union[int, BitVec]]]:
         """
 
         :param item:
@@ -108,14 +121,18 @@ class Memory:
                 raise IndexError("Invalid Memory Slice")
             if step is None:
                 step = 1
-            return [self[i] for i in range(start, stop, step)]
+            return [cast(Union[int, BitVec], self[i]) for i in range(start, stop, step)]
 
         try:
             return self._memory[item]
         except IndexError:
             return 0
 
-    def __setitem__(self, key: Union[int, slice], value: Union[BitVec, int, list]):
+    def __setitem__(
+        self,
+        key: Union[int, slice],
+        value: Union[BitVec, int, List[Union[int, BitVec]]],
+    ):
         """
 
         :param key:
@@ -130,13 +147,13 @@ class Memory:
                 raise IndexError("Invalid Memory Slice")
             if step is None:
                 step = 1
-
+            assert type(value) == list
             for i in range(0, stop - start, step):
-                self[start + i] = value[i]
+                self[start + i] = cast(List[Union[int, BitVec]], value)[i]
 
         else:
             if isinstance(value, int):
                 assert 0 <= value <= 0xFF
             if isinstance(value, BitVec):
                 assert value.size() == 8
-            self._memory[key] = value
+            self._memory[key] = cast(Union[int, BitVec], value)
diff --git a/mythril/laser/ethereum/state/world_state.py b/mythril/laser/ethereum/state/world_state.py
index 7bcd06b4..9b5bdcaa 100644
--- a/mythril/laser/ethereum/state/world_state.py
+++ b/mythril/laser/ethereum/state/world_state.py
@@ -1,11 +1,14 @@
 """This module contains a representation of the EVM's world state."""
 from copy import copy
 from random import randint
-from typing import List, Iterator
+from typing import Dict, List, Iterator, Optional, TYPE_CHECKING
 
 from mythril.laser.ethereum.state.account import Account
 from mythril.laser.ethereum.state.annotation import StateAnnotation
 
+if TYPE_CHECKING:
+    from mythril.laser.ethereum.cfg import Node
+
 
 class WorldState:
     """The WorldState class represents the world state as described in the
@@ -19,8 +22,8 @@ class WorldState:
         :param transaction_sequence:
         :param annotations:
         """
-        self.accounts = {}
-        self.node = None
+        self.accounts = {}  # type: Dict[str, Account]
+        self.node = None  # type: Optional['Node']
         self.transaction_sequence = transaction_sequence or []
         self._annotations = annotations or []
 
diff --git a/mythril/laser/ethereum/strategy/basic.py b/mythril/laser/ethereum/strategy/basic.py
index 6627241c..5930f4e6 100644
--- a/mythril/laser/ethereum/strategy/basic.py
+++ b/mythril/laser/ethereum/strategy/basic.py
@@ -1,5 +1,6 @@
 """This module implements basic symbolic execution search strategies."""
 from random import randrange
+from typing import List
 
 from mythril.laser.ethereum.state.global_state import GlobalState
 from . import BasicSearchStrategy
@@ -13,7 +14,10 @@ except ImportError:
     from random import random
     from bisect import bisect
 
-    def choices(population, weights=None):
+    # TODO: Remove ignore after this has been fixed: https://github.com/python/mypy/issues/1297
+    def choices(  # type: ignore
+        population: List, weights: List[int] = None
+    ) -> List[int]:
         """Returns a random element out of the population based on weight.
 
         If the relative weights or cumulative weights are not specified,
@@ -21,7 +25,7 @@ except ImportError:
         """
         if weights is None:
             return [population[int(random() * len(population))]]
-        cum_weights = accumulate(weights)
+        cum_weights = list(accumulate(weights))
         return [
             population[
                 bisect(cum_weights, random() * cum_weights[-1], 0, len(population) - 1)
diff --git a/mythril/laser/ethereum/svm.py b/mythril/laser/ethereum/svm.py
index 7b2a39d8..491719ea 100644
--- a/mythril/laser/ethereum/svm.py
+++ b/mythril/laser/ethereum/svm.py
@@ -4,7 +4,7 @@ from collections import defaultdict
 from copy import copy
 from datetime import datetime, timedelta
 from functools import reduce
-from typing import Callable, Dict, List, Tuple, Union
+from typing import Callable, Dict, DefaultDict, List, Tuple, Union
 
 from mythril.laser.ethereum.cfg import NodeFlags, Node, Edge, JumpType
 from mythril.laser.ethereum.evm_exceptions import StackUnderflowException
@@ -56,7 +56,7 @@ class LaserEVM:
         transaction_count=2,
         requires_statespace=True,
         enable_iprof=False,
-    ):
+    ) -> None:
         """
 
         :param accounts:
@@ -73,12 +73,12 @@ class LaserEVM:
         self.world_state = world_state
         self.open_states = [world_state]
 
-        self.coverage = {}
+        self.coverage = {}  # type: Dict[str, Tuple[int, List[bool]]]
 
         self.total_states = 0
         self.dynamic_loader = dynamic_loader
 
-        self.work_list = []
+        self.work_list = []  # type: List[GlobalState]
         self.strategy = strategy(self.work_list, max_depth)
         self.max_depth = max_depth
         self.transaction_count = transaction_count
@@ -88,14 +88,15 @@ class LaserEVM:
 
         self.requires_statespace = requires_statespace
         if self.requires_statespace:
-            self.nodes = {}
-            self.edges = []
+            self.nodes = {}  # type: Dict[int, Node]
+            self.edges = []  # type: List[Edge]
 
-        self.time = None
+        self.time = None  # type: datetime
 
-        self.pre_hooks = defaultdict(list)
-        self.post_hooks = defaultdict(list)
-        self._add_world_state_hooks = []
+        self.pre_hooks = defaultdict(list)  # type: DefaultDict[str, List[Callable]]
+        self.post_hooks = defaultdict(list)  # type: DefaultDict[str, List[Callable]]
+
+        self._add_world_state_hooks = []  # type: List[Callable]
         self.iprof = InstructionProfiler() if enable_iprof else None
 
         log.info("LASER EVM initialized with dynamic loader: " + str(dynamic_loader))
@@ -153,11 +154,8 @@ class LaserEVM:
                 self.total_states,
             )
         for code, coverage in self.coverage.items():
-            cov = (
-                reduce(lambda sum_, val: sum_ + 1 if val else sum_, coverage[1])
-                / float(coverage[0])
-                * 100
-            )
+            cov = sum(coverage[1]) / float(coverage[0]) * 100
+
             log.info("Achieved {:.2f}% coverage for code: {}".format(cov, code))
 
         if self.iprof is not None:
@@ -198,9 +196,7 @@ class LaserEVM:
         """
         total_covered_instructions = 0
         for _, cv in self.coverage.items():
-            total_covered_instructions += reduce(
-                lambda sum_, val: sum_ + 1 if val else sum_, cv[1]
-            )
+            total_covered_instructions += sum(cv[1])
         return total_covered_instructions
 
     def exec(self, create=False, track_gas=False) -> Union[List[GlobalState], None]:
@@ -210,7 +206,7 @@ class LaserEVM:
         :param track_gas:
         :return:
         """
-        final_states = []
+        final_states = []  # type: List[GlobalState]
         for global_state in self.strategy:
             if (
                 self.create_timeout
@@ -385,10 +381,10 @@ class LaserEVM:
         instruction_index = global_state.mstate.pc
 
         if code not in self.coverage.keys():
-            self.coverage[code] = [
+            self.coverage[code] = (
                 number_of_instructions,
                 [False] * number_of_instructions,
-            ]
+            )
 
         self.coverage[code][1][instruction_index] = True
 
diff --git a/mythril/laser/ethereum/transaction/transaction_models.py b/mythril/laser/ethereum/transaction/transaction_models.py
index a915c0e3..def9a494 100644
--- a/mythril/laser/ethereum/transaction/transaction_models.py
+++ b/mythril/laser/ethereum/transaction/transaction_models.py
@@ -3,7 +3,7 @@ execution."""
 
 import array
 from z3 import ExprRef
-from typing import Union
+from typing import Union, Optional, cast
 
 from mythril.laser.ethereum.state.calldata import ConcreteCalldata
 from mythril.laser.ethereum.state.account import Account
@@ -17,20 +17,20 @@ from mythril.laser.smt import symbol_factory
 _next_transaction_id = 0
 
 
-def get_next_transaction_id() -> int:
+def get_next_transaction_id() -> str:
     """
 
     :return:
     """
     global _next_transaction_id
     _next_transaction_id += 1
-    return _next_transaction_id
+    return str(_next_transaction_id)
 
 
 class TransactionEndSignal(Exception):
     """Exception raised when a transaction is finalized."""
 
-    def __init__(self, global_state: GlobalState, revert=False):
+    def __init__(self, global_state: GlobalState, revert=False) -> None:
         self.global_state = global_state
         self.revert = revert
 
@@ -42,7 +42,7 @@ class TransactionStartSignal(Exception):
         self,
         transaction: Union["MessageCallTransaction", "ContractCreationTransaction"],
         op_code: str,
-    ):
+    ) -> None:
         self.transaction = transaction
         self.op_code = op_code
 
@@ -56,14 +56,14 @@ class BaseTransaction:
         callee_account: Account = None,
         caller: ExprRef = None,
         call_data=None,
-        identifier=None,
+        identifier: Optional[str] = None,
         gas_price=None,
         gas_limit=None,
         origin=None,
         code=None,
         call_value=None,
         init_call_data=True,
-    ):
+    ) -> None:
         assert isinstance(world_state, WorldState)
         self.world_state = world_state
         self.id = identifier or get_next_transaction_id()
@@ -85,7 +85,7 @@ class BaseTransaction:
         self.caller = caller
         self.callee_account = callee_account
         if call_data is None and init_call_data:
-            self.call_data = SymbolicCalldata(self.id)
+            self.call_data = SymbolicCalldata(self.id)  # type: BaseCalldata
         else:
             self.call_data = (
                 call_data
@@ -99,7 +99,7 @@ class BaseTransaction:
             else symbol_factory.BitVecSym("callvalue{}".format(identifier), 256)
         )
 
-        self.return_data = None
+        self.return_data = None  # type: str
 
     def initial_global_state_from_environment(self, environment, active_function):
         """
@@ -117,7 +117,7 @@ class BaseTransaction:
 class MessageCallTransaction(BaseTransaction):
     """Transaction object models an transaction."""
 
-    def __init__(self, *args, **kwargs):
+    def __init__(self, *args, **kwargs) -> None:
         super().__init__(*args, **kwargs)
 
     def initial_global_state(self) -> GlobalState:
@@ -149,8 +149,9 @@ class MessageCallTransaction(BaseTransaction):
 class ContractCreationTransaction(BaseTransaction):
     """Transaction object models an transaction."""
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs, init_call_data=False)
+    def __init__(self, *args, **kwargs) -> None:
+        # Remove ignore after https://github.com/python/mypy/issues/4335 is fixed
+        super().__init__(*args, **kwargs, init_call_data=False)  # type: ignore
         # TODO: set correct balance for new account
         self.callee_account = self.callee_account or self.world_state.create_account(
             0, concrete_storage=True
diff --git a/mythril/laser/ethereum/util.py b/mythril/laser/ethereum/util.py
index 880e04c4..9cb5d950 100644
--- a/mythril/laser/ethereum/util.py
+++ b/mythril/laser/ethereum/util.py
@@ -1,9 +1,10 @@
 """This module contains various utility conversion functions and constants for
 LASER."""
 import re
-from typing import Dict, List, Union
+from typing import Dict, List, Union, TYPE_CHECKING, cast
 
-import sha3 as _sha3
+if TYPE_CHECKING:
+    from mythril.laser.ethereum.state.machine_state import MachineState
 
 from mythril.laser.smt import BitVec, Bool, Expression, If, simplify, symbol_factory
 
@@ -12,15 +13,6 @@ TT256M1 = 2 ** 256 - 1
 TT255 = 2 ** 255
 
 
-def sha3(seed: str) -> bytes:
-    """
-
-    :param seed:
-    :return:
-    """
-    return _sha3.keccak_256(bytes(seed)).digest()
-
-
 def safe_decode(hex_encoded_string: str) -> bytes:
     """
 
@@ -83,18 +75,16 @@ def pop_bitvec(state: "MachineState") -> BitVec:
 
     item = state.stack.pop()
 
-    if type(item) == Bool:
+    if isinstance(item, Bool):
         return If(
-            item, symbol_factory.BitVecVal(1, 256), symbol_factory.BitVecVal(0, 256)
+            cast(Bool, item),
+            symbol_factory.BitVecVal(1, 256),
+            symbol_factory.BitVecVal(0, 256),
         )
-    elif type(item) == bool:
-        if item:
-            return symbol_factory.BitVecVal(1, 256)
-        else:
-            return symbol_factory.BitVecVal(0, 256)
-    elif type(item) == int:
+    elif isinstance(item, int):
         return symbol_factory.BitVecVal(item, 256)
     else:
+        item = cast(BitVec, item)
         return simplify(item)
 
 
@@ -116,8 +106,12 @@ def get_concrete_int(item: Union[int, Expression]) -> int:
             raise TypeError("Symbolic boolref encountered")
         return value
 
+    assert False, "Unhandled type {} encountered".format(str(type(item)))
+
 
-def concrete_int_from_bytes(concrete_bytes: bytes, start_index: int) -> int:
+def concrete_int_from_bytes(
+    concrete_bytes: Union[List[Union[BitVec, int]], bytes], start_index: int
+) -> int:
     """
 
     :param concrete_bytes:
@@ -130,7 +124,8 @@ def concrete_int_from_bytes(concrete_bytes: bytes, start_index: int) -> int:
     ]
     integer_bytes = concrete_bytes[start_index : start_index + 32]
 
-    return int.from_bytes(integer_bytes, byteorder="big")
+    # The below statement is expected to fail in some circumstances whose error is caught
+    return int.from_bytes(integer_bytes, byteorder="big")  # type: ignore
 
 
 def concrete_int_to_bytes(val):
diff --git a/mythril/laser/smt/bitvec.py b/mythril/laser/smt/bitvec.py
index feeac40b..8347352c 100644
--- a/mythril/laser/smt/bitvec.py
+++ b/mythril/laser/smt/bitvec.py
@@ -11,6 +11,7 @@ Annotations = List[Any]
 
 # fmt: off
 
+
 class BitVec(Expression[z3.BitVecRef]):
     """A bit vector symbol."""
 
@@ -139,6 +140,24 @@ class BitVec(Expression[z3.BitVecRef]):
         union = self.annotations + other.annotations
         return Bool(self.raw > other.raw, annotations=union)
 
+    def __le__(self, other: "BitVec") -> Bool:
+        """Create a signed less than expression.
+
+        :param other:
+        :return:
+        """
+        union = self.annotations + other.annotations
+        return Bool(self.raw <= other.raw, annotations=union)
+
+    def __ge__(self, other: "BitVec") -> Bool:
+        """Create a signed greater than expression.
+
+        :param other:
+        :return:
+        """
+        union = self.annotations + other.annotations
+        return Bool(self.raw >= other.raw, annotations=union)
+
     # MYPY: fix complains about overriding __eq__
     def __eq__(self, other: Union[int, "BitVec"]) -> Bool:  # type: ignore
         """Create an equality expression.
diff --git a/mythril/laser/smt/bool.py b/mythril/laser/smt/bool.py
index c82e4f1f..9fa097e4 100644
--- a/mythril/laser/smt/bool.py
+++ b/mythril/laser/smt/bool.py
@@ -1,7 +1,7 @@
 """This module provides classes for an SMT abstraction of boolean
 expressions."""
 
-from typing import Union, cast
+from typing import Union, cast, List
 
 import z3
 
@@ -81,13 +81,13 @@ class Bool(Expression[z3.BoolRef]):
             return False
 
 
-def And(*args: Bool) -> Bool:
+def And(*args: Union[Bool, bool]) -> Bool:
     """Create an And expression."""
     union = []
-    args = [arg if isinstance(arg, Bool) else Bool(arg) for arg in args]
-    for arg in args:
+    args_list = [arg if isinstance(arg, Bool) else Bool(arg) for arg in args]
+    for arg in args_list:
         union.append(arg.annotations)
-    return Bool(z3.And([a.raw for a in args]), union)
+    return Bool(z3.And([a.raw for a in args_list]), union)
 
 
 def Or(a: Bool, b: Bool) -> Bool:
diff --git a/mythril/laser/smt/expression.py b/mythril/laser/smt/expression.py
index 2ed166c7..8e9e697e 100644
--- a/mythril/laser/smt/expression.py
+++ b/mythril/laser/smt/expression.py
@@ -46,7 +46,10 @@ class Expression(Generic[T]):
         return repr(self.raw)
 
 
-def simplify(expression: Expression) -> Expression:
+G = TypeVar("G", bound=Expression)
+
+
+def simplify(expression: G) -> G:
     """Simplify the expression .
 
     :param expression:
diff --git a/mythril/support/loader.py b/mythril/support/loader.py
index d55bc185..6e434439 100644
--- a/mythril/support/loader.py
+++ b/mythril/support/loader.py
@@ -22,7 +22,7 @@ class DynLoader:
         self.contract_loading = contract_loading
         self.storage_loading = storage_loading
 
-    def read_storage(self, contract_address, index):
+    def read_storage(self, contract_address: str, index: int):
         """
 
         :param contract_address:
diff --git a/mythril/support/signatures.py b/mythril/support/signatures.py
index 530f0137..e0deb9ea 100644
--- a/mythril/support/signatures.py
+++ b/mythril/support/signatures.py
@@ -7,7 +7,7 @@ import sqlite3
 import time
 from collections import defaultdict
 from subprocess import PIPE, Popen
-from typing import List
+from typing import List, Set, DefaultDict, Dict
 
 from mythril.exceptions import CompilerError
 
@@ -45,7 +45,7 @@ def synchronized(sync_lock):
 class Singleton(type):
     """A metaclass type implementing the singleton pattern."""
 
-    _instances = {}
+    _instances = dict()  # type: Dict[Singleton, Singleton]
 
     @synchronized(lock)
     def __call__(cls, *args, **kwargs):
@@ -60,6 +60,7 @@ class Singleton(type):
         """
         if cls not in cls._instances:
             cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
+
         return cls._instances[cls]
 
 
@@ -120,12 +121,12 @@ class SignatureDB(object, metaclass=Singleton):
         :param path:
         """
         self.enable_online_lookup = enable_online_lookup
-        self.online_lookup_miss = set()
+        self.online_lookup_miss = set()  # type: Set[str]
         self.online_lookup_timeout = 0
 
         # if we're analysing a Solidity file, store its hashes
         # here to prevent unnecessary lookups
-        self.solidity_sigs = defaultdict(list)
+        self.solidity_sigs = defaultdict(list)  # type: DefaultDict[str, List[str]]
         if path is None:
             self.path = os.environ.get("MYTHRIL_DIR") or os.path.join(
                 os.path.expanduser("~"), ".mythril"
@@ -225,7 +226,7 @@ class SignatureDB(object, metaclass=Singleton):
                 return text_sigs
         except FourByteDirectoryOnlineLookupError as fbdole:
             # wait at least 2 mins to try again
-            self.online_lookup_timeout = time.time() + 2 * 60
+            self.online_lookup_timeout = int(time.time()) + 2 * 60
             log.warning("Online lookup failed, not retrying for 2min: %s", fbdole)
             return []
 
diff --git a/mythril/support/support_utils.py b/mythril/support/support_utils.py
index 9fe90a8f..b437d795 100644
--- a/mythril/support/support_utils.py
+++ b/mythril/support/support_utils.py
@@ -1,10 +1,11 @@
 """This module contains utility functions for the Mythril support package."""
+from typing import Dict
 
 
 class Singleton(type):
     """A metaclass type implementing the singleton pattern."""
 
-    _instances = {}
+    _instances = {}  # type: Dict
 
     def __call__(cls, *args, **kwargs):
         """Delegate the call to an existing resource or a a new one.
diff --git a/setup.py b/setup.py
index 82a6fbed..1f0a0a02 100755
--- a/setup.py
+++ b/setup.py
@@ -98,7 +98,7 @@ setup(
         "persistent>=4.2.0",
         "ethereum-input-decoder>=0.2.2",
     ],
-    tests_require=["pytest>=3.6.0", "pytest_mock", "pytest-cov"],
+    tests_require=["mypy", "pytest>=3.6.0", "pytest_mock", "pytest-cov"],
     python_requires=">=3.5",
     extras_require={},
     package_data={"mythril.analysis.templates": ["*"], "mythril.support.assets": ["*"]},
diff --git a/tox.ini b/tox.ini
index aeab98ca..93ee48a2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -19,12 +19,14 @@ basepython = python3.6
 setenv =
     COVERAGE_FILE = .coverage.{envname}
 deps =
+    mypy
     pytest
     pytest-mock
     pytest-cov
 passenv = MYTHRIL_DIR = {homedir}
 whitelist_externals = mkdir
 commands =
+    mypy --follow-imports=silent --warn-unused-ignores --ignore-missing-imports --no-strict-optional mythril
     mkdir -p {toxinidir}/tests/testdata/outputs_current/
     mkdir -p {toxinidir}/tests/testdata/outputs_current_laser_result/
     py.test -v \
@@ -35,6 +37,8 @@ commands =
         --junitxml={toxworkdir}/output/{envname}/junit.xml \
         {posargs}
 
+
+
 [coverage:report]
 omit =
     *__init__.py