diff --git a/RockLib.Messaging.Tests/FakeMessageHandler.cs b/RockLib.Messaging.Tests/FakeMessageHandler.cs
index 2c6aec89..d784cf99 100644
--- a/RockLib.Messaging.Tests/FakeMessageHandler.cs
+++ b/RockLib.Messaging.Tests/FakeMessageHandler.cs
@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace RockLib.Messaging.Tests
 {
@@ -6,9 +7,10 @@ public class FakeMessageHandler : IMessageHandler
     {
         public List<(IReceiver Receiver, IReceiverMessage Message)> ReceivedMessages { get; } = new List<(IReceiver, IReceiverMessage)>();
 
-        public void OnMessageReceived(IReceiver receiver, IReceiverMessage message)
+        public Task OnMessageReceivedAsync(IReceiver receiver, IReceiverMessage message)
         {
             ReceivedMessages.Add((receiver, message));
+            return Task.FromResult(0);
         }
     }
 }
diff --git a/RockLib.Messaging.Tests/ForwardingMessageHandlerTests.cs b/RockLib.Messaging.Tests/ForwardingMessageHandlerTests.cs
index 5a6348ae..5332095e 100644
--- a/RockLib.Messaging.Tests/ForwardingMessageHandlerTests.cs
+++ b/RockLib.Messaging.Tests/ForwardingMessageHandlerTests.cs
@@ -1,6 +1,7 @@
 using FluentAssertions;
 using NUnit.Framework;
 using RockLib.Messaging.Testing;
+using System.Threading.Tasks;
 
 namespace RockLib.Messaging.Tests
 {
@@ -8,7 +9,7 @@ namespace RockLib.Messaging.Tests
     public class ForwardingMessageHandlerTests
     {
         [Test]
-        public void OnMessageReceivedCallsInnerHandlerOnMessageReceivedWithForwardingReceiverMessage()
+        public async Task OnMessageReceivedCallsInnerHandlerOnMessageReceivedWithForwardingReceiverMessage()
         {
             var receiver = new FakeReceiver();
             var forwardingReceiver = new ForwardingReceiver("foo", receiver);
@@ -18,7 +19,7 @@ public void OnMessageReceivedCallsInnerHandlerOnMessageReceivedWithForwardingRec
 
             var message = new FakeReceiverMessage("Hello, world!");
 
-            handler.OnMessageReceived(receiver, message);
+            await handler.OnMessageReceivedAsync(receiver, message);
 
             messageHandler.ReceivedMessages.Should().ContainSingle();
             messageHandler.ReceivedMessages[0].Receiver.Should().BeSameAs(forwardingReceiver);
diff --git a/RockLib.Messaging.Tests/ReceiverExtensionsTests.cs b/RockLib.Messaging.Tests/ReceiverExtensionsTests.cs
new file mode 100644
index 00000000..958106e7
--- /dev/null
+++ b/RockLib.Messaging.Tests/ReceiverExtensionsTests.cs
@@ -0,0 +1,82 @@
+using NUnit.Framework;
+using RockLib.Messaging.Testing;
+using System.Threading.Tasks;
+
+namespace RockLib.Messaging.Tests
+{
+    [TestFixture]
+    public class ReceiverExtensionsTests
+    {
+        [Test]
+        public async Task TheCallbackPassedToStart1IsInvokedWhenAMessageIsReceived()
+        {
+            var receiver = new FakeReceiver();
+
+            var received = false;
+
+            receiver.Start(async m =>
+            {
+                received = true;
+                await m.AcknowledgeAsync();
+            });
+
+            await receiver.MessageHandler.OnMessageReceivedAsync(receiver, new FakeReceiverMessage("Hello, world!"));
+
+            Assert.True(received);
+        }
+
+        [Test]
+        public async Task TheCallbackPassedToStart2IsInvokedWhenAMessageIsReceived()
+        {
+            var receiver = new FakeReceiver();
+
+            var received = false;
+
+            receiver.Start(m =>
+            {
+                received = true;
+                m.Acknowledge();
+            });
+
+            await receiver.MessageHandler.OnMessageReceivedAsync(receiver, new FakeReceiverMessage("Hello, world!"));
+
+            Assert.True(received);
+        }
+
+        [Test]
+        public async Task TheCallbackPassedToStart3IsInvokedWhenAMessageIsReceived()
+        {
+            var receiver = new FakeReceiver();
+
+            var received = false;
+
+            receiver.Start(async (r, m) =>
+            {
+                received = true;
+                await m.AcknowledgeAsync();
+            });
+
+            await receiver.MessageHandler.OnMessageReceivedAsync(receiver, new FakeReceiverMessage("Hello, world!"));
+
+            Assert.True(received);
+        }
+
+        [Test]
+        public async Task TheCallbackPassedToStart4IsInvokedWhenAMessageIsReceived()
+        {
+            var receiver = new FakeReceiver();
+
+            var received = false;
+
+            receiver.Start((r, m) =>
+            {
+                received = true;
+                m.Acknowledge();
+            });
+
+            await receiver.MessageHandler.OnMessageReceivedAsync(receiver, new FakeReceiverMessage("Hello, world!"));
+
+            Assert.True(received);
+        }
+    }
+}
diff --git a/RockLib.Messaging/ForwardingMessageHandler.cs b/RockLib.Messaging/ForwardingMessageHandler.cs
index 48912497..75d59528 100644
--- a/RockLib.Messaging/ForwardingMessageHandler.cs
+++ b/RockLib.Messaging/ForwardingMessageHandler.cs
@@ -1,4 +1,6 @@
-namespace RockLib.Messaging
+using System.Threading.Tasks;
+
+namespace RockLib.Messaging
 {
     /// <summary>
     /// A decorator for the <see cref="IMessageHandler"/> interface that forwards
@@ -30,7 +32,7 @@ internal ForwardingMessageHandler(ForwardingReceiver forwardingReceiver, IMessag
         /// <summary>
         /// Handles a received message.
         /// <para>
-        /// When invoked, this method invokes the <see cref="IMessageHandler.OnMessageReceived"/>
+        /// When invoked, this method invokes the <see cref="IMessageHandler.OnMessageReceivedAsync"/>
         /// method of the <see cref="MessageHandler"/> property. It passes the
         /// <see cref="ForwardingReceiver"/> property as the <c>receiver</c> argument and
         /// a new <see cref="ForwardingReceiverMessage"/> decorator as the <c>message</c>
@@ -39,7 +41,7 @@ internal ForwardingMessageHandler(ForwardingReceiver forwardingReceiver, IMessag
         /// </summary>
         /// <param name="receiver">The instance of <see cref="IReceiver"/> that received the message.</param>
         /// <param name="message">The message that was received.</param>
-        public void OnMessageReceived(IReceiver receiver, IReceiverMessage message) =>
-            MessageHandler.OnMessageReceived(ForwardingReceiver, new ForwardingReceiverMessage(ForwardingReceiver, message));
+        public Task OnMessageReceivedAsync(IReceiver receiver, IReceiverMessage message) =>
+            MessageHandler.OnMessageReceivedAsync(ForwardingReceiver, new ForwardingReceiverMessage(ForwardingReceiver, message));
     }
 }
diff --git a/RockLib.Messaging/ForwardingReceiver.cs b/RockLib.Messaging/ForwardingReceiver.cs
index 97991824..0b6e0138 100644
--- a/RockLib.Messaging/ForwardingReceiver.cs
+++ b/RockLib.Messaging/ForwardingReceiver.cs
@@ -152,7 +152,7 @@ public ForwardingReceiver(string name, IReceiver receiver,
 
         /// <summary>
         /// Gets or sets the message handler for this receiver. When set, the receiver is started
-        /// and will invoke the value's <see cref="IMessageHandler.OnMessageReceived"/> method
+        /// and will invoke the value's <see cref="IMessageHandler.OnMessageReceivedAsync"/> method
         /// when messages are received.
         /// <para>
         /// When set, this property sets the <see cref="IReceiver.MessageHandler"/> of the
diff --git a/RockLib.Messaging/IMessageHandler.cs b/RockLib.Messaging/IMessageHandler.cs
index a1295656..cd5b00a0 100644
--- a/RockLib.Messaging/IMessageHandler.cs
+++ b/RockLib.Messaging/IMessageHandler.cs
@@ -1,4 +1,6 @@
-namespace RockLib.Messaging
+using System.Threading.Tasks;
+
+namespace RockLib.Messaging
 {
     /// <summary>
     /// Defines an object that handles the messages received by an instance
@@ -11,6 +13,6 @@ public interface IMessageHandler
         /// </summary>
         /// <param name="receiver">The instance of <see cref="IReceiver"/> that received the message.</param>
         /// <param name="message">The message that was received.</param>
-        void OnMessageReceived(IReceiver receiver, IReceiverMessage message);
+        Task OnMessageReceivedAsync(IReceiver receiver, IReceiverMessage message);
     }
 }
\ No newline at end of file
diff --git a/RockLib.Messaging/IReceiver.cs b/RockLib.Messaging/IReceiver.cs
index 6e19df5a..d13b808c 100644
--- a/RockLib.Messaging/IReceiver.cs
+++ b/RockLib.Messaging/IReceiver.cs
@@ -15,7 +15,7 @@ public interface IReceiver : IDisposable
 
         /// <summary>
         /// Gets or sets the message handler for this receiver. When set, the receiver is started
-        /// and will invoke the value's <see cref="IMessageHandler.OnMessageReceived"/> method
+        /// and will invoke the value's <see cref="IMessageHandler.OnMessageReceivedAsync"/> method
         /// when messages are received.
         /// </summary>
         /// <remarks>
diff --git a/RockLib.Messaging/OnMessageReceivedDelegate.cs b/RockLib.Messaging/OnMessageReceivedDelegate.cs
index 05b75022..80d5b691 100644
--- a/RockLib.Messaging/OnMessageReceivedDelegate.cs
+++ b/RockLib.Messaging/OnMessageReceivedDelegate.cs
@@ -1,9 +1,18 @@
-namespace RockLib.Messaging
+using System.Threading.Tasks;
+
+namespace RockLib.Messaging
 {
     /// <summary>
-    /// Defines a function that handles a received message.
+    /// Defines a synchronous function that handles a received message.
     /// </summary>
     /// <param name="receiver">The instance of <see cref="IReceiver"/> that received the message.</param>
     /// <param name="message">The message that was received.</param>
     public delegate void OnMessageReceivedDelegate(IReceiver receiver, IReceiverMessage message);
+
+    /// <summary>
+    /// Defines an asynchronous function that handles a received message.
+    /// </summary>
+    /// <param name="receiver">The instance of <see cref="IReceiver"/> that received the message.</param>
+    /// <param name="message">The message that was received.</param>
+    public delegate Task OnMessageReceivedAsyncDelegate(IReceiver receiver, IReceiverMessage message);
 }
diff --git a/RockLib.Messaging/Receiver.cs b/RockLib.Messaging/Receiver.cs
index 30271d89..6438e7dd 100644
--- a/RockLib.Messaging/Receiver.cs
+++ b/RockLib.Messaging/Receiver.cs
@@ -26,7 +26,7 @@ protected Receiver(string name)
 
         /// <summary>
         /// Gets or sets the message handler for this receiver. When set, the receiver is started
-        /// and will invoke the value's <see cref="IMessageHandler.OnMessageReceived"/> method
+        /// and will invoke the value's <see cref="IMessageHandler.OnMessageReceivedAsync"/> method
         /// when messages are received.
         /// </summary>
         public IMessageHandler MessageHandler
diff --git a/RockLib.Messaging/ReceiverExtensions.cs b/RockLib.Messaging/ReceiverExtensions.cs
index c3bc7e39..049f3f67 100644
--- a/RockLib.Messaging/ReceiverExtensions.cs
+++ b/RockLib.Messaging/ReceiverExtensions.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Threading.Tasks;
 
 namespace RockLib.Messaging
 {
@@ -26,7 +27,29 @@ public static void Start(this IReceiver receiver, Action<IReceiverMessage> onMes
         public static void Start(this IReceiver receiver, OnMessageReceivedDelegate onMessageReceived)
         {
             if (onMessageReceived == null) throw new ArgumentNullException(nameof(onMessageReceived));
-            receiver.Start(new DelegateMessageHandler(onMessageReceived));
+            receiver.Start(new SyncDelegateMessageHandler(onMessageReceived));
+        }
+
+        /// <summary>
+        /// Start listening for messages and handle them using the specified callback function.
+        /// </summary>
+        /// <param name="receiver">The receiver to start.</param>
+        /// <param name="onMessageReceivedAsync">A function that is invoked when a message is received.</param>
+        public static void Start(this IReceiver receiver, Func<IReceiverMessage, Task> onMessageReceivedAsync)
+        {
+            if (onMessageReceivedAsync == null) throw new ArgumentNullException(nameof(onMessageReceivedAsync));
+            receiver.Start((_, message) => onMessageReceivedAsync(message));
+        }
+
+        /// <summary>
+        /// Start listening for messages and handle them using the specified callback function.
+        /// </summary>
+        /// <param name="receiver">The receiver to start.</param>
+        /// <param name="onMessageReceivedAsync">A function that is invoked when a message is received.</param>
+        public static void Start(this IReceiver receiver, OnMessageReceivedAsyncDelegate onMessageReceivedAsync)
+        {
+            if (onMessageReceivedAsync == null) throw new ArgumentNullException(nameof(onMessageReceivedAsync));
+            receiver.Start(new AsyncDelegateMessageHandler(onMessageReceivedAsync));
         }
 
         /// <summary>
@@ -44,15 +67,40 @@ public static void Start(this IReceiver receiver, IMessageHandler messageHandler
             receiver.MessageHandler = messageHandler ?? throw new ArgumentNullException(nameof(messageHandler));
         }
 
-        private class DelegateMessageHandler : IMessageHandler
+        private class SyncDelegateMessageHandler : IMessageHandler
         {
             private readonly OnMessageReceivedDelegate _onMessageReceived;
 
-            public DelegateMessageHandler(OnMessageReceivedDelegate onMessageReceived) =>
+            public SyncDelegateMessageHandler(OnMessageReceivedDelegate onMessageReceived) =>
                 _onMessageReceived = onMessageReceived;
 
-            public void OnMessageReceived(IReceiver receiver, IReceiverMessage message) =>
-                _onMessageReceived(receiver, message);
+            public Task OnMessageReceivedAsync(IReceiver receiver, IReceiverMessage message)
+            {
+                var source = new TaskCompletionSource<int>();
+
+                try
+                {
+                    _onMessageReceived(receiver, message);
+                    source.SetResult(0);
+                }
+                catch (Exception ex)
+                {
+                    source.SetException(ex);
+                }
+
+                return source.Task;
+            }
+        }
+
+        private class AsyncDelegateMessageHandler : IMessageHandler
+        {
+            private readonly OnMessageReceivedAsyncDelegate _onMessageReceivedAsync;
+
+            public AsyncDelegateMessageHandler(OnMessageReceivedAsyncDelegate onMessageReceivedAsync) =>
+                _onMessageReceivedAsync = onMessageReceivedAsync;
+
+            public Task OnMessageReceivedAsync(IReceiver receiver, IReceiverMessage message) =>
+                _onMessageReceivedAsync(receiver, message);
         }
     }
 }
\ No newline at end of file