diff --git a/PENDING.md b/PENDING.md
index 05dd59ee0..dd4fe4bb6 100644
--- a/PENDING.md
+++ b/PENDING.md
@@ -43,7 +43,8 @@ IMPROVEMENTS
 * Gaia
 
 * SDK
-  * \#1277 Complete bank module specification
+ - \#1277 Complete bank module specification
+ - \#2963 Complete auth module specification
   * \#2914 No longer withdraw validator rewards on bond/unbond, but rather move
   the rewards to the respective validator's pools.
 
diff --git a/docs/spec/auth/README.md b/docs/spec/auth/README.md
new file mode 100644
index 000000000..6db6db226
--- /dev/null
+++ b/docs/spec/auth/README.md
@@ -0,0 +1,29 @@
+# Auth module specification
+
+## Abstract
+
+This document specifies the auth module of the Cosmos SDK.
+
+The auth module is responsible for specifying the base transaction and account types
+for an application, since the SDK itself is agnostic to these particulars. It contains
+the ante handler, where all basic transaction validity checks (signatures, nonces, auxiliary fields)
+are performed, and exposes the account keeper, which allows other modules to read, write, and modify accounts.
+
+This module will be used in the Cosmos Hub.
+
+## Contents
+
+1. **[State](state.md)**
+    1. [Accounts](state.md#accounts)
+        1. [Account Interface](state.md#account-interface)
+        1. [Base Account](state.md#baseaccount)
+        1. [Vesting Account](state.md#vestingaccount)
+1. **[Types](types.md)**
+    1. [StdFee](types.md#stdfee)
+    1. [StdSignature](types.md#stdsignature)
+    1. [StdTx](types.md#stdtx)
+    1. [StdSignDoc](types.md#stdsigndoc)
+1. **[Keepers](keepers.md)**
+    1. [AccountKeeper](keepers.md#account-keeper)
+1. **[Handlers](handlers.md)**
+    1. [Ante Handler](handlers.md#ante-handler)
diff --git a/docs/spec/auth/handlers.md b/docs/spec/auth/handlers.md
new file mode 100644
index 000000000..2f8909c63
--- /dev/null
+++ b/docs/spec/auth/handlers.md
@@ -0,0 +1,38 @@
+## Handlers
+
+The auth module presently has no transaction handlers of its own, but does expose
+the special `AnteHandler`, used for performing basic validity checks on a transaction,
+such that it could be thrown out of the mempool. Note that the ante handler is called on
+`CheckTx`, but *also* on `DeliverTx`, as Tendermint proposers presently have the ability
+to include in their proposed block transactions which fail `CheckTx`.
+
+### Ante Handler
+
+```golang
+anteHandler(ak AccountKeeper, fck FeeCollectionKeeper, tx sdk.Tx)
+  if !tx.(StdTx)
+    fail with "not a StdTx"
+
+  if isCheckTx and tx.Fee < config.SubjectiveMinimumFee
+    fail with "insufficient fee for mempool inclusion"
+
+  if tx.ValidateBasic() != nil
+    fail with "tx failed ValidateBasic"
+
+  if tx.Fee > 0
+    account = GetAccount(tx.GetSigners()[0])
+    coins := acount.GetCoins()
+    if coins < tx.Fee
+      fail with "insufficient fee to pay for transaction"
+    account.SetCoins(coins - tx.Fee)
+    fck.AddCollectedFees(tx.Fee)
+
+  for index, signature in tx.GetSignatures()
+    account = GetAccount(tx.GetSigners()[index])
+    bytesToSign := StdSignBytes(chainID, acc.GetAccountNumber(),
+      acc.GetSequence(), tx.Fee, tx.Msgs, tx.Memo)
+    if !signature.Verify(bytesToSign)
+      fail with "invalid signature"
+
+  return
+```
diff --git a/docs/spec/auth/keepers.md b/docs/spec/auth/keepers.md
new file mode 100644
index 000000000..27611decd
--- /dev/null
+++ b/docs/spec/auth/keepers.md
@@ -0,0 +1,39 @@
+## Keepers
+
+The auth module only exposes one keeper, the account keeper, which can be used to read and write accounts.
+
+### Account Keeper
+
+Presently only one fully-permissioned account keeper is exposed, which has the ability to both read and write
+all fields of all accounts, and to iterate over all stored accounts.
+
+```golang
+type AccountKeeper interface {
+  // Return a new account with the next account number and the specified address. Does not save the new account to the store.
+  NewAccountWithAddress(AccAddress) Account
+
+  // Return a new account with the next account number. Does not save the new account to the store.
+  NewAccount(Account) Account
+
+  // Retrieve an account from the store
+  GetAccount(AccAddress) Account
+
+  // Set an account in the store
+  SetAccount(Account)
+
+  // Remove an account from the store
+  RemoveAccount(Account)
+
+  // Iterate over all accounts, calling the provided function. Stop iteraiton when it returns false.
+  IterateAccounts(func(Account) (bool))
+
+  // Fetch the public key of an account at a specified address
+  GetPubKey(AccAddress) PubKey
+
+  // Fetch the sequence of an account at a specified address
+  GetSequence(AccAddress) uint64
+
+  // Fetch the next account number, and increment the internal counter
+  GetNextAccountNumber() uint64
+}
+```
diff --git a/docs/spec/auth/state.md b/docs/spec/auth/state.md
index e69de29bb..29b5a93ab 100644
--- a/docs/spec/auth/state.md
+++ b/docs/spec/auth/state.md
@@ -0,0 +1,58 @@
+## State
+
+### Accounts
+
+Accounts contain authentication information for a uniquely identified external user of an SDK blockchain,
+including public key, address, and account number / sequence number for replay protection. For efficiency,
+since account balances must also be fetched to pay fees, account structs also store the balance of a user
+as `sdk.Coins`.
+
+Accounts are exposed externally as an interface, and stored internally as
+either a base account or vesting account. Module clients wishing to add more
+account types may do so.
+
+- `0x01 | Address -> amino(account)`
+
+#### Account Interface
+
+The account interface exposes methods to read and write standard account information.
+Note that all of these methods operate on an account struct confirming to the interface
+- in order to write the account to the store, the account keeper will need to be used.
+
+```golang
+type Account interface {
+  GetAddress() AccAddress
+  SetAddress(AccAddress)
+
+  GetPubKey() PubKey
+  SetPubKey(PubKey)
+
+  GetAccountNumber() uint64
+  SetAccountNumber(uint64)
+
+  GetSequence() uint64
+  SetSequence(uint64)
+
+  GetCoins() Coins
+  SetCoins(Coins)
+}
+```
+
+#### Base Account
+
+A base account is the simplest and most common account type, which just stores all requisite
+fields directly in a struct.
+
+```golang
+type BaseAccount struct {
+  Address       AccAddress
+  Coins         Coins
+  PubKey        PubKey
+  AccountNumber uint64
+  Sequence      uint64
+}
+```
+
+#### Vesting Account
+
+See [Vesting](vesting.md).
diff --git a/docs/spec/auth/transactions.md b/docs/spec/auth/transactions.md
deleted file mode 100644
index e69de29bb..000000000
diff --git a/docs/spec/auth/types.md b/docs/spec/auth/types.md
new file mode 100644
index 000000000..30c5ac8b1
--- /dev/null
+++ b/docs/spec/auth/types.md
@@ -0,0 +1,65 @@
+## Types
+
+Besides accounts (specified in [State](state.md)), the types exposed by the auth module
+are `StdFee`, the combination of an amount and gas limit, `StdSignature`, the combination
+of an optional public key and a cryptographic signature as a byte array, `StdTx`,
+a struct which implements the `sdk.Tx` interface using `StdFee` and `StdSignature`, and
+`StdSignDoc`, a replay-prevention structure for `StdTx` which transaction senders must sign over.
+
+### StdFee
+
+A `StdFee` is simply the combination of a fee amount, in any number of denominations,
+and a gas limit (where dividing the amount by the gas limit gives a "gas price").
+
+```golang
+type StdFee struct {
+  Amount Coins
+  Gas    uint64
+}
+```
+
+### StdSignature
+
+A `StdSignature` is the combination of an optional public key and a cryptographic signature
+as a byte array. The SDK is agnostic to particular key or signature formats and supports any
+supported by the `PubKey` interface.
+
+```golang
+type StdSignature struct {
+  PubKey    PubKey
+  Signature []byte
+}
+```
+
+### StdTx
+
+A `StdTx` is a struct which implements the `sdk.Tx` interface, and is likely to be generic
+enough to serve the purposes of many Cosmos SDK blockchains.
+
+```golang
+type StdTx struct {
+  Msgs        []sdk.Msg
+  Fee         StdFee  
+  Signatures  []StdSignature
+  Memo        string
+}
+```
+
+### StdSignDoc
+
+A `StdSignDoc` is a replay-prevention structure to be signed over, which ensures that
+any submitted transaction (which is simply a signature over a particular bytestring)
+will only be executable once on a particular blockchain.
+
+`json.RawMessage` is preferred over using the SDK types for future compatibility.
+
+```golang
+type StdSignDoc struct {
+  AccountNumber uint64
+  ChainID       string
+  Fee           json.RawMessage
+  Memo          string
+  Msgs          []json.RawMessage
+  Sequence      uint64
+}
+```
diff --git a/x/auth/keeper.go b/x/auth/keeper.go
index deecaf2b2..18e82c206 100644
--- a/x/auth/keeper.go
+++ b/x/auth/keeper.go
@@ -6,7 +6,12 @@ import (
 	"github.com/tendermint/tendermint/crypto"
 )
 
-var globalAccountNumberKey = []byte("globalAccountNumber")
+var (
+	// Prefix for account-by-address store
+	AddressStoreKeyPrefix = []byte{0x01}
+
+	globalAccountNumberKey = []byte("globalAccountNumber")
+)
 
 // This AccountKeeper encodes/decodes accounts using the
 // go-amino (binary) encoding/decoding library.
@@ -61,7 +66,7 @@ func (am AccountKeeper) NewAccount(ctx sdk.Context, acc Account) Account {
 
 // Turn an address to key used to get it from the account store
 func AddressStoreKey(addr sdk.AccAddress) []byte {
-	return append([]byte("account:"), addr.Bytes()...)
+	return append(AddressStoreKeyPrefix, addr.Bytes()...)
 }
 
 // Implements sdk.AccountKeeper.
@@ -93,7 +98,7 @@ func (am AccountKeeper) RemoveAccount(ctx sdk.Context, acc Account) {
 // Implements sdk.AccountKeeper.
 func (am AccountKeeper) IterateAccounts(ctx sdk.Context, process func(Account) (stop bool)) {
 	store := ctx.KVStore(am.key)
-	iter := sdk.KVStorePrefixIterator(store, []byte("account:"))
+	iter := sdk.KVStorePrefixIterator(store, AddressStoreKeyPrefix)
 	defer iter.Close()
 	for {
 		if !iter.Valid() {