diff --git a/src/HttpAsyncClient.php b/src/HttpAsyncClient.php
new file mode 100644
index 0000000..737ee63
--- /dev/null
+++ b/src/HttpAsyncClient.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace Http\Client;
+
+use Psr\Http\Message\RequestInterface;
+
+/**
+ * Sends a PSR-7 Request in an asynchronous way by returning a Promise.
+ *
+ * @author Joel Wurtz <joel.wurtz@gmail.com>
+ */
+interface HttpAsyncClient
+{
+    /**
+     * Sends a PSR-7 request in an asynchronous way.
+     *
+     * @param RequestInterface $request
+     *
+     * @return Promise
+     *
+     * @throws Exception
+     */
+    public function sendAsyncRequest(RequestInterface $request);
+}
diff --git a/src/HttpClient.php b/src/HttpClient.php
index 525f9e0..fa66c2c 100644
--- a/src/HttpClient.php
+++ b/src/HttpClient.php
@@ -2,7 +2,6 @@
 
 namespace Http\Client;
 
-use Http\Client\Exception\BatchException;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 
diff --git a/src/Promise.php b/src/Promise.php
new file mode 100644
index 0000000..575bc6e
--- /dev/null
+++ b/src/Promise.php
@@ -0,0 +1,83 @@
+<?php
+
+namespace Http\Client;
+
+use Psr\Http\Message\ResponseInterface;
+
+/**
+ * Promise represents a response that may not be available yet, but will be resolved at some point in future.
+ * It acts like a proxy to the actual response.
+ *
+ * This interface is an extension of the promises/a+ specification https://promisesaplus.com/
+ * Value is replaced by an object where its class implement a Psr\Http\Message\RequestInterface.
+ * Reason is replaced by an object where its class implement a Http\Client\Exception.
+ *
+ * @author Joel Wurtz <joel.wurtz@gmail.com>
+ */
+interface Promise
+{
+    /**
+     * Pending state, promise has not been fulfilled or rejected.
+     */
+    const PENDING   = "pending";
+
+    /**
+     * Fulfilled state, promise has been fulfilled with a ResponseInterface object.
+     */
+    const FULFILLED = "fulfilled";
+
+    /**
+     * Rejected state, promise has been rejected with an Exception object.
+     */
+    const REJECTED  = "rejected";
+
+    /**
+     * Add behavior for when the promise is resolved or rejected (response will be available, or error happens).
+     *
+     * If you do not care about one of the cases, you can set the corresponding callable to null
+     * The callback will be called when the response or exception arrived and never more than once.
+     *
+     * @param callable $onFulfilled Called when a response will be available.
+     * @param callable $onRejected  Called when an error happens.
+     *
+     * You must always return the Response in the interface or throw an Exception.
+     *
+     * @return Promise Always returns a new promise which is resolved with value of the executed callback (onFulfilled / onRejected).
+     */
+    public function then(callable $onFulfilled = null, callable $onRejected = null);
+
+    /**
+     * Get the state of the promise, one of PENDING, FULFILLED or REJECTED
+     *
+     * @return int
+     */
+    public function getState();
+
+    /**
+     * Return the value of the promise (fulfilled).
+     *
+     * @return ResponseInterface Response Object only when the Promise is fulfilled.
+     *
+     * @throws \LogicException When the promise is not fulfilled.
+     */
+    public function getResponse();
+
+    /**
+     * Return the reason of the promise (rejected).
+     *
+     * @return Exception Exception Object only when the Promise is rejected.
+     *
+     * If the exception is an instance of Http\Client\Exception\HttpException it will contain
+     * the response object with the status code and the http reason.
+     *
+     * @throws \LogicException When the promise is not rejected.
+     */
+    public function getException();
+
+    /**
+     * Wait for the promise to be fulfilled or rejected.
+     *
+     * When this method returns, the request has been resolved and the appropriate callable has terminated.
+     */
+    public function wait();
+}