diff --git a/lib/bcoin.js b/lib/bcoin.js
index bfe0b477..0f5f2b02 100644
--- a/lib/bcoin.js
+++ b/lib/bcoin.js
@@ -56,6 +56,7 @@ bcoin.ramdisk = require('./bcoin/ramdisk');
 bcoin.chainblock = require('./bcoin/chainblock');
 bcoin.chaindb = require('./bcoin/chaindb');
 bcoin.chain = require('./bcoin/chain');
+bcoin.mempool = require('./bcoin/mempool');
 bcoin.keypair = require('./bcoin/keypair');
 bcoin.address = require('./bcoin/address');
 bcoin.wallet = require('./bcoin/wallet');
diff --git a/lib/bcoin/chainblock.js b/lib/bcoin/chainblock.js
index 70713196..51fdfb53 100644
--- a/lib/bcoin/chainblock.js
+++ b/lib/bcoin/chainblock.js
@@ -20,6 +20,9 @@ var fs = bcoin.fs;
  */
 
 function ChainBlock(chain, data) {
+  if (!(this instanceof ChainBlock))
+    return new ChainBlock(chain, data);
+
   this.chain = chain;
   this.hash = data.hash;
   this.version = data.version;
diff --git a/lib/bcoin/chaindb.js b/lib/bcoin/chaindb.js
index eb165cb7..04a36a23 100644
--- a/lib/bcoin/chaindb.js
+++ b/lib/bcoin/chaindb.js
@@ -23,7 +23,7 @@ var BLOCK_SIZE = bcoin.chainblock.BLOCK_SIZE;
 
 function ChainDB(chain, options) {
   if (!(this instanceof ChainDB))
-    return new ChainDB(chain);
+    return new ChainDB(chain, options);
 
   if (!options)
     options = {};
diff --git a/lib/bcoin/mempool.js b/lib/bcoin/mempool.js
new file mode 100644
index 00000000..6bb2f31e
--- /dev/null
+++ b/lib/bcoin/mempool.js
@@ -0,0 +1,264 @@
+/**
+ * mempool.js - mempool for bcoin
+ * Copyright (c) 2014-2015, Fedor Indutny (MIT License)
+ * https://github.com/indutny/bcoin
+ */
+
+var inherits = require('inherits');
+var EventEmitter = require('events').EventEmitter;
+
+var bcoin = require('../bcoin');
+var bn = require('bn.js');
+var constants = bcoin.protocol.constants;
+var network = bcoin.protocol.network;
+var utils = bcoin.utils;
+var assert = utils.assert;
+var fs = bcoin.fs;
+
+/**
+ * Mempool
+ */
+
+function Mempool(pool, options) {
+  if (!(this instanceof Mempool))
+    return new Mempool(pool, options);
+
+  if (!options)
+    options = {};
+
+  this.options = options;
+  this.pool = pool;
+  this.storage = bcoin.db;
+
+  this.txs = {};
+  this.prevout = {};
+  this.size = 0;
+  this.count = 0;
+  this.locked = false;
+
+  this._init();
+}
+
+Mempool.prototype._init = function _init() {
+  var self = this;
+
+  // Remove now-mined transactions
+  this.pool.on('block', function(block) {
+    block.txs.forEach(function(tx) {
+      var mtx = self.get(tx);
+      if (!mtx)
+        return;
+
+      mtx.ps = 0;
+      mtx.ts = block.ts;
+      mtx.block = block.hash('hex');
+
+      self.remove(mtx);
+    });
+  });
+};
+
+Mempool.prototype.get = function get(hash) {
+  if (hash instanceof bcoin.tx)
+    hash = hash.hash('hex');
+  return this.txs[hash];
+};
+
+Mempool.prototype.getAll = function getAll(hash) {
+  return Object.keys(this.txs).map(function(key) {
+    return this.txs[key];
+  }, this);
+};
+
+Mempool.prototype.has = function has(hash) {
+  return !!this.get(hash);
+};
+
+Mempool.prototype.add = function add(tx, peer, callback) {
+  var self = this;
+  var hash = tx.hash('hex');
+
+  assert(tx.ts === 0);
+
+  callback = utils.asyncify(callback);
+
+  if (this.locked)
+    return callback(new Error('Mempool is locked.'));
+
+  if (this.count >= 50000)
+    return callback(new Error('Mempool is full.'));
+
+  if (this.size >= 20 * 1024 * 1024)
+    return callback(new Error('Mempool is full.'));
+
+  if (this.txs[hash])
+    return callback(new Error('Already have TX.'));
+
+  this._lockTX(tx);
+
+  this.storage.fillTX(tx, function(err) {
+    var i, input, dup, height, ts, priority;
+
+    self._unlockTX(tx);
+
+    if (err)
+      return callback(err);
+
+    if (!tx.hasPrevout()) {
+      pool.setMisbehavior(peer, 100);
+      return callback(new Error('Previous outputs not found.'));
+    }
+
+    if (!tx.isStandard()) {
+      pool.setMisbehavior(peer, 100);
+      return callback(new Error('TX is not standard.'));
+    }
+
+    if (!tx.isStandardInputs()) {
+      pool.setMisbehavior(peer, 100);
+      return callback(new Error('TX inputs are not standard.'));
+    }
+
+    if (tx.getOutputValue().cmp(tx.getInputValue()) > 0) {
+      pool.setMisbehavior(peer, 100);
+      return callback(new Error('TX is spending coins that it does not have.'));
+    }
+
+    height = self.pool.chain.height() + 1;
+    ts = utils.now();
+    if (!tx.isFinal(height, ts)) {
+      pool.setMisbehavior(peer, 100);
+      return callback(new Error('TX is not final.'));
+    }
+
+    for (i = 0; i < tx.inputs.length; i++) {
+      input = tx.inputs[i];
+      if (input.output.spent) {
+        pool.setMisbehavior(peer, 100);
+        return callback(new Error('TX is spending old outputs.'));
+      }
+      dup = self.prevout[input.prevout.hash];
+      if (dup) {
+        // Replace-by-fee
+        if (input.sequence === 0xffffffff - 1) {
+          if (dup.getFee().cmp(tx.getFee()) < 0) {
+            self.remove(dup);
+            continue;
+          }
+        }
+        pool.setMisbehavior(peer, 100);
+        return callback(new Error('TX is double spending.'));
+      }
+    }
+
+    for (i = 0; i < tx.outputs.length; i++) {
+      output = tx.outputs[i];
+      if (output.value.cmpn(0) < 0) {
+        pool.setMisbehavior(peer, 100);
+        return callback(new Error('TX is spending negative coins.'));
+      }
+    }
+
+    if (!tx.verify(true)) {
+      pool.setMisbehavior(peer, 100);
+      return callback(new Error('TX did not verify.'));
+    }
+
+    for (i = 0; i < tx.inputs.length; i++) {
+      input = tx.inputs[i];
+      self.prevout[input.prevout.hash] = tx;
+    }
+
+    // Possibly do something bitcoinxt-like here with priority
+    priority = tx.getPriority();
+
+    self.txs[hash] = tx;
+    self.count++;
+    self.size += tx.getSize();
+
+    self.storage.saveMempoolTX(tx, function(err) {
+      if (err)
+        return callback(err);
+
+      return callback();
+    });
+  });
+};
+
+// Lock a tx to prevent race conditions
+Mempool.prototype._lockTX = function _lockTX(tx) {
+  var hash = tx.hash('hex');
+  var i, input;
+
+  if (!this.txs[hash])
+    this.txs[hash] = tx;
+
+  for (i = 0; i < tx.inputs.length; i++) {
+    input = tx.inputs[i];
+    if (!this.prevout[input.prevout.hash])
+      this.prevout[input.prevout.hash] = tx;
+  }
+};
+
+Mempool.prototype._unlockTX = function _unlockTX(tx) {
+  var hash = tx.hash('hex');
+  var i, input;
+
+  if (this.txs[hash] === tx)
+    delete this.txs[hash];
+
+  for (i = 0; i < tx.inputs.length; i++) {
+    input = tx.inputs[i];
+    if (this.prevout[input.prevout.hash] === tx)
+      delete this.prevout[input.prevout.hash];
+  }
+};
+
+Mempool.prototype.remove = function remove(hash, callback) {
+  var self = this;
+  var tx, input;
+
+  callback = utils.asyncify(callback);
+
+  if (hash instanceof bcoin.tx)
+    hash = hash.hash('hex');
+
+  tx = this.txs[hash];
+
+  if (!tx)
+    return callback(new Error('TX does not exist in mempool.'));
+
+  for (i = 0; i < tx.inputs.length; i++) {
+    input = tx.inputs[i];
+    if (this.prevout[input.prevout.hash] === tx)
+      delete this.prevout[input.prevout.hash];
+  }
+
+  delete this.txs[hash];
+
+  this.count--;
+  this.size -= tx.getSize();
+
+  this.storage.removeMempoolTX(tx, function(err) {
+    if (err)
+      return callback(err);
+
+    return callback();
+  });
+};
+
+// Need to lock the mempool when
+// downloading a new block.
+Mempool.prototype.lock = function lock() {
+  this.locked = true;
+};
+
+Mempool.prototype.unlock = function unlock() {
+  this.locked = false;
+};
+
+/**
+ * Expose
+ */
+
+module.exports = Mempool;