diff --git a/app/scripts/background.js b/app/scripts/background.js
index 6550e8944..38b871bb5 100644
--- a/app/scripts/background.js
+++ b/app/scripts/background.js
@@ -1,3 +1,7 @@
+/**
+ * @file The entry point for the web extension singleton process.
+ */
+
 const urlUtil = require('url')
 const endOfStream = require('end-of-stream')
 const pump = require('pump')
@@ -61,6 +65,90 @@ initialize().catch(log.error)
 // setup metamask mesh testing container
 setupMetamaskMeshMetrics()
 
+/**
+ * An object representing a transaction, in whatever state it is in.
+ * @typedef TransactionMeta
+ *
+ * @property {number} id - An internally unique tx identifier.
+ * @property {number} time - Time the tx was first suggested, in unix epoch time (ms).
+ * @property {string} status - The current transaction status (unapproved, signed, submitted, dropped, failed, rejected), as defined in `tx-state-manager.js`.
+ * @property {string} metamaskNetworkId - The transaction's network ID, used for EIP-155 compliance.
+ * @property {boolean} loadingDefaults - TODO: Document
+ * @property {Object} txParams - The tx params as passed to the network provider.
+ * @property {Object[]} history - A history of mutations to this TransactionMeta object.
+ * @property {boolean} gasPriceSpecified - True if the suggesting dapp specified a gas price, prevents auto-estimation.
+ * @property {boolean} gasLimitSpecified - True if the suggesting dapp specified a gas limit, prevents auto-estimation.
+ * @property {string} estimatedGas - A hex string represented the estimated gas limit required to complete the transaction.
+ * @property {string} origin - A string representing the interface that suggested the transaction.
+ * @property {Object} nonceDetails - A metadata object containing information used to derive the suggested nonce, useful for debugging nonce issues.
+ * @property {string} rawTx - A hex string of the final signed transaction, ready to submit to the network.
+ * @property {string} hash - A hex string of the transaction hash, used to identify the transaction on the network.
+ * @property {number} submittedTime - The time the transaction was submitted to the network, in Unix epoch time (ms).
+ */
+
+/**
+ * The data emitted from the MetaMaskController.store EventEmitter, also used to initialize the MetaMaskController. Available in UI on React state as state.metamask.
+ * @typedef MetaMaskState
+ * @property {boolean} isInitialized - Whether the first vault has been created.
+ * @property {boolean} isUnlocked - Whether the vault is currently decrypted and accounts are available for selection.
+ * @property {boolean} isAccountMenuOpen - Represents whether the main account selection UI is currently displayed.
+ * @property {boolean} isMascara - True if the current context is the extensionless MetaMascara project.
+ * @property {boolean} isPopup - Returns true if the current view is an externally-triggered notification.
+ * @property {string} rpcTarget - DEPRECATED - The URL of the current RPC provider.
+ * @property {Object} identities - An object matching lower-case hex addresses to Identity objects with "address" and "name" (nickname) keys.
+ * @property {Object} unapprovedTxs - An object mapping transaction hashes to unapproved transactions.
+ * @property {boolean} noActiveNotices - False if there are notices the user should confirm before using the application.
+ * @property {Array} frequentRpcList - A list of frequently used RPCs, including custom user-provided ones.
+ * @property {Array} addressBook - A list of previously sent to addresses.
+ * @property {address} selectedTokenAddress - Used to indicate if a token is globally selected. Should be deprecated in favor of UI-centric token selection.
+ * @property {Object} tokenExchangeRates - Info about current token prices.
+ * @property {Array} tokens - Tokens held by the current user, including their balances.
+ * @property {Object} send - TODO: Document
+ * @property {Object} coinOptions - TODO: Document
+ * @property {boolean} useBlockie - Indicates preferred user identicon format. True for blockie, false for Jazzicon.
+ * @property {Object} featureFlags - An object for optional feature flags.
+ * @property {string} networkEndpointType - TODO: Document
+ * @property {boolean} isRevealingSeedWords - True if seed words are currently being recovered, and should be shown to user.
+ * @property {boolean} welcomeScreen - True if welcome screen should be shown.
+ * @property {string} currentLocale - A locale string matching the user's preferred display language.
+ * @property {Object} provider - The current selected network provider.
+ * @property {string} provider.rpcTarget - The address for the RPC API, if using an RPC API.
+ * @property {string} provider.type - An identifier for the type of network selected, allows MetaMask to use custom provider strategies for known networks.
+ * @property {string} network - A stringified number of the current network ID.
+ * @property {Object} accounts - An object mapping lower-case hex addresses to objects with "balance" and "address" keys, both storing hex string values.
+ * @property {hex} currentBlockGasLimit - The most recently seen block gas limit, in a lower case hex prefixed string.
+ * @property {TransactionMeta[]} selectedAddressTxList - An array of transactions associated with the currently selected account.
+ * @property {Object} unapprovedMsgs - An object of messages associated with the currently selected account, mapping a unique ID to the options.
+ * @property {number} unapprovedMsgCount - The number of messages in unapprovedMsgs.
+ * @property {Object} unapprovedPersonalMsgs - An object of messages associated with the currently selected account, mapping a unique ID to the options.
+ * @property {number} unapprovedPersonalMsgCount - The number of messages in unapprovedPersonalMsgs.
+ * @property {Object} unapprovedTypedMsgs - An object of messages associated with the currently selected account, mapping a unique ID to the options.
+ * @property {number} unapprovedTypedMsgCount - The number of messages in unapprovedTypedMsgs.
+ * @property {string[]} keyringTypes - An array of unique keyring identifying strings, representing available strategies for creating accounts.
+ * @property {Keyring[]} keyrings - An array of keyring descriptions, summarizing the accounts that are available for use, and what keyrings they belong to.
+ * @property {Object} computedBalances - Maps accounts to their balances, accounting for balance changes from pending transactions.
+ * @property {string} currentAccountTab - A view identifying string for displaying the current displayed view, allows user to have a preferred tab in the old UI (between tokens and history).
+ * @property {string} selectedAddress - A lower case hex string of the currently selected address.
+ * @property {string} currentCurrency - A string identifying the user's preferred display currency, for use in showing conversion rates.
+ * @property {number} conversionRate - A number representing the current exchange rate from the user's preferred currency to Ether.
+ * @property {number} conversionDate - A unix epoch date (ms) for the time the current conversion rate was last retrieved.
+ * @property {Object} infuraNetworkStatus - An object of infura network status checks.
+ * @property {Block[]} recentBlocks - An array of recent blocks, used to calculate an effective but cheap gas price.
+ * @property {Array} shapeShiftTxList - An array of objects describing shapeshift exchange attempts.
+ * @property {Array} lostAccounts - TODO: Remove this feature. A leftover from the version-3 migration where our seed-phrase library changed to fix a bug where some accounts were mis-generated, but we recovered the old accounts as "lost" instead of losing them.
+ * @property {boolean} forgottenPassword - Returns true if the user has initiated the password recovery screen, is recovering from seed phrase.
+ */
+
+/**
+ * @typedef VersionedData
+ * @property {MetaMaskState} data - The data emitted from MetaMask controller, or used to initialize it.
+ * @property {Number} version - The latest migration version that has been run.
+ */
+
+/**
+ * Initializes the MetaMask controller, and sets up all platform configuration.
+ * @returns {Promise} Setup complete.
+ */
 async function initialize () {
   const initState = await loadStateFromPersistence()
   const initLangCode = await getFirstPreferredLangCode()
@@ -72,6 +160,11 @@ async function initialize () {
 // State and Persistence
 //
 
+/**
+ * Loads any stored data, prioritizing the latest storage strategy.
+ * Migrates that data schema in case it was last loaded on an older version.
+ * @returns {Promise<MetaMaskState>} Last data emitted from previous instance of MetaMask.
+ */
 async function loadStateFromPersistence () {
   // migrations
   const migrator = new Migrator({ migrations })
@@ -134,6 +227,16 @@ async function loadStateFromPersistence () {
   return versionedData.data
 }
 
+/**
+ * Initializes the MetaMask Controller with any initial state and default language.
+ * Configures platform-specific error reporting strategy.
+ * Streams emitted state updates to platform-specific storage strategy.
+ * Creates platform listeners for new Dapps/Contexts, and sets up their data connections to the controller.
+ *
+ * @param {Object} initState - The initial state to start the controller with, matches the state that is emitted from the controller.
+ * @param {String} initLangCode - The region code for the language preferred by the current user.
+ * @returns {Promise} After setup is complete.
+ */
 function setupController (initState, initLangCode) {
   //
   // MetaMask Controller
@@ -172,6 +275,11 @@ function setupController (initState, initLangCode) {
     }
   )
 
+  /**
+   * Assigns the given state to the versioned object (with metadata), and returns that.
+   * @param {Object} state - The state object as emitted by the MetaMaskController.
+   * @returns {VersionedData} The state object wrapped in an object that includes a metadata key.
+   */
   function versionifyData (state) {
     versionedData.data = state
     return versionedData
@@ -208,6 +316,18 @@ function setupController (initState, initLangCode) {
     return popupIsOpen || Boolean(Object.keys(openMetamaskTabsIDs).length) || notificationIsOpen
   }
 
+  /**
+   * A runtime.Port object, as provided by the browser:
+   * @link https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/runtime/Port
+   * @typedef Port
+   * @type Object
+   */
+
+  /**
+   * Connects a Port to the MetaMask controller via a multiplexed duplex stream.
+   * This method identifies trusted (MetaMask) interfaces, and connects them differently from untrusted (web pages).
+   * @param {Port} remotePort - The port provided by a new context.
+   */
   function connectRemote (remotePort) {
     const processName = remotePort.name
     const isMetaMaskInternalProcess = metamaskInternalProcessHash[processName]
@@ -261,7 +381,10 @@ function setupController (initState, initLangCode) {
   controller.messageManager.on('updateBadge', updateBadge)
   controller.personalMessageManager.on('updateBadge', updateBadge)
 
-  // plugin badge text
+  /**
+   * Updates the Web Extension's "badge" number, on the little fox in the toolbar.
+   * The number reflects the current number of pending transactions or message signatures needing user approval.
+   */
   function updateBadge () {
     var label = ''
     var unapprovedTxCount = controller.txController.getUnapprovedTxCount()
@@ -283,7 +406,9 @@ function setupController (initState, initLangCode) {
 // Etc...
 //
 
-// popup trigger
+/**
+ * Opens the browser popup for user confirmation
+ */
 function triggerUi () {
   extension.tabs.query({ active: true }, tabs => {
     const currentlyActiveMetamaskTab = Boolean(tabs.find(tab => openMetamaskTabsIDs[tab.id]))