diff --git a/src/AbstractPool.php b/src/AbstractPool.php
new file mode 100644
index 0000000..44fe55c
--- /dev/null
+++ b/src/AbstractPool.php
@@ -0,0 +1,293 @@
+<?php
+
+namespace Amp\Sql;
+
+use function Amp\call;
+use Amp\CallableMaker;
+use function Amp\coroutine;
+use Amp\Deferred;
+use Amp\Loop;
+use Amp\Promise;
+
+abstract class AbstractPool implements Pool
+{
+    use CallableMaker;
+
+    /** @var Connector */
+    private $connector;
+
+    /** @var ConnectionConfig */
+    private $config;
+
+    /** @var int */
+    private $maxConnections;
+
+    /** @var \SplQueue */
+    private $idle;
+
+    /** @var \SplObjectStorage */
+    private $connections;
+
+    /** @var Promise|null */
+    private $promise;
+
+    /** @var Deferred|null */
+    private $deferred;
+
+    /** @var int Number of pending connections. */
+    private $pending = 0;
+
+    /** @var bool */
+    private $closed = false;
+
+    /** @var string */
+    private $timeoutWatcher;
+
+    /** @var int */
+    private $idleTimeout = Pool::DEFAULT_IDLE_TIMEOUT;
+
+    /** @var callable */
+    private $prepare;
+
+    /** @var int */
+    private $lastUsedAt;
+
+    /**
+     * @param ConnectionConfig $config
+     * @param int $maxConnections
+     * @param Connector $connector
+     *
+     * @throws \Error If $maxConnections is less than 1.
+     */
+    public function __construct(
+        ConnectionConfig $config,
+        int $maxConnections = Pool::DEFAULT_MAX_CONNECTIONS,
+        Connector $connector = null
+    ) {
+        $this->connector = $connector ?? $this->defaultConnector();
+        $this->config = $config;
+        $this->maxConnections = $maxConnections;
+
+        if ($this->maxConnections < 1) {
+            throw new \Error("Pool must contain at least one connection");
+        }
+
+        $this->connections = $connections = new \SplObjectStorage;
+        $this->idle = $idle = new \SplQueue;
+        $this->prepare = coroutine($this->callableFromInstanceMethod("doPrepare"));
+
+        $idleTimeout = &$this->idleTimeout;
+
+        $this->timeoutWatcher = Loop::repeat(1000, static function () use (&$idleTimeout, $connections, $idle) {
+            $now = \time();
+            while (!$idle->isEmpty()) {
+                /** @var Connection $connection */
+                $connection = $idle->bottom();
+
+                if ($connection->lastUsedAt() + $idleTimeout > $now) {
+                    return;
+                }
+
+                // Close connection and remove it from the pool.
+                $idle->shift();
+                $connections->detach($connection);
+                $connection->close();
+            }
+        });
+
+        Loop::unreference($this->timeoutWatcher);
+
+        $this->lastUsedAt = \time();
+    }
+
+    public function __destruct()
+    {
+        Loop::cancel($this->timeoutWatcher);
+    }
+
+    public function query(string $sql): Promise
+    {
+        return call(function () use ($sql) {
+            /** @var Connection $connection */
+            $connection = yield from $this->pop();
+
+            try {
+                $result = yield $connection->query($sql);
+            } catch (\Throwable $exception) {
+                $this->push($connection);
+                throw $exception;
+            }
+
+            if ($result instanceof Operation) {
+                $result->onDestruct(function () use ($connection) {
+                    $this->push($connection);
+                });
+            } else {
+                $this->push($connection);
+            }
+
+            $this->lastUsedAt = \time();
+
+            return $result;
+        });
+    }
+
+    public function prepare(string $sql): Promise
+    {
+        return call(function () use ($sql) {
+            $statement = yield from $this->doPrepare($sql);
+
+            $this->lastUsedAt = \time();
+
+            return $this->newPooledStatement($this, $statement, $this->prepare);
+        });
+    }
+
+    public function execute(string $sql, array $params = []): Promise
+    {
+        return call(function () use ($sql, $params) {
+            /** @var Connection $connection */
+            $connection = yield from $this->pop();
+
+            try {
+                $result = yield $connection->execute($sql, $params);
+            } catch (\Throwable $exception) {
+                $this->push($connection);
+                throw $exception;
+            }
+
+            if ($result instanceof Operation) {
+                $result->onDestruct(function () use ($connection) {
+                    $this->push($connection);
+                });
+            } else {
+                $this->push($connection);
+            }
+
+            $this->lastUsedAt = \time();
+
+            return $result;
+        });
+    }
+
+    public function isAlive(): bool
+    {
+        return !$this->closed;
+    }
+
+    public function close()
+    {
+        // TODO: Implement close() method.
+    }
+
+    public function lastUsedAt(): int
+    {
+        return $this->lastUsedAt;
+    }
+
+    public function transaction(int $isolation = Transaction::ISOLATION_COMMITTED): Promise
+    {
+        return call(function () use ($isolation) {
+            /** @var Connection $connection */
+            $connection = yield from $this->pop();
+
+            try {
+                /** @var Transaction $transaction */
+                $transaction = yield $connection->transaction($isolation);
+            } catch (\Throwable $exception) {
+                $this->push($connection);
+                throw $exception;
+            }
+
+            $transaction->onDestruct(function () use ($connection) {
+                $this->push($connection);
+            });
+
+            $this->lastUsedAt = \time();
+
+            return $transaction;
+        });
+    }
+
+    /**
+     * Extracts an idle connection from the pool. The connection is completely removed from the pool and cannot be
+     * put back into the pool. Useful for operations where connection state must be changed.
+     *
+     * @return Promise<Connection>
+     */
+    public function extractConnection(): Promise
+    {
+        return call(function () {
+            $connection = yield from $this->pop();
+            $this->connections->detach($connection);
+
+            $this->lastUsedAt = \time();
+
+            return $connection;
+        });
+    }
+
+    public function getConnectionCount(): int
+    {
+        return $this->connections->count();
+    }
+
+    public function getIdleConnectionCount(): int
+    {
+        return $this->idle->count();
+    }
+
+    public function getMaxConnections(): int
+    {
+        return $this->maxConnections;
+    }
+
+    public function getIdleTimeout(): int
+    {
+        return $this->idleTimeout;
+    }
+
+    public function setIdleTimeout(int $timeout)
+    {
+        if ($timeout < 1) {
+            throw new \Error("Timeout must be greater than or equal to 1");
+        }
+
+        $this->idleTimeout = $timeout;
+    }
+
+    private function doPrepare(string $sql): \Generator
+    {
+        /** @var Connection $connection */
+        $connection = yield from $this->pop();
+
+        try {
+            /** @var Statement $statement */
+            $statement = yield $connection->prepare($sql);
+        } catch (\Throwable $exception) {
+            $this->push($connection);
+            throw $exception;
+        }
+
+        \assert(
+            $statement instanceof Operation,
+            Statement::class . " instances returned from connections must implement " . Operation::class
+        );
+
+        $statement->onDestruct(function () use ($connection) {
+            $this->push($connection);
+        });
+
+        $this->lastUsedAt = \time();
+
+        return $statement;
+    }
+
+    abstract protected function defaultConnector(): Connector;
+
+    abstract protected function newPooledStatement(Pool $pool, Statement $statement, callable $prepare): Statement;
+
+    abstract protected function pop(): \Generator;
+
+    abstract protected function push(Connection $connection);
+}