diff --git a/README.md b/README.md
index 973e9ea..ca33b56 100644
--- a/README.md
+++ b/README.md
@@ -97,4 +97,8 @@ Extends `Error` to indicate that an entity could not be found.
 
 ### `UnauthorizedError`
 
-Extends `Error` to indicate that the action being performed is not authorized.
\ No newline at end of file
+Extends `Error` to indicate that the action being performed is not authorized.
+
+### `ConflictError`
+
+Extends `Error` to indicate the action cannot be completed due to the existence of a conflicting entity.
\ No newline at end of file
diff --git a/src/Winton.DomainModelling.Abstractions/ConflictError.cs b/src/Winton.DomainModelling.Abstractions/ConflictError.cs
new file mode 100644
index 0000000..18d4458
--- /dev/null
+++ b/src/Winton.DomainModelling.Abstractions/ConflictError.cs
@@ -0,0 +1,22 @@
+// Copyright (c) Winton. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
+
+namespace Winton.DomainModelling
+{
+    /// <inheritdoc />
+    /// <summary>
+    ///     An error indicating that a conflicting entity exists.
+    /// </summary>
+    public class ConflictError : Error
+    {
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="ConflictError" /> class.
+        /// </summary>
+        /// <param name="detail">The detail that describes the error.</param>
+        /// <returns>A new instance of <see cref="ConflictError" />.</returns>
+        public ConflictError(string detail)
+            : base("Conflict", detail)
+        {
+        }
+    }
+}