diff --git a/src/mcp/types.py b/src/mcp/types.py
index 2c27f83..4e1628c 100644
--- a/src/mcp/types.py
+++ b/src/mcp/types.py
@@ -285,6 +285,8 @@ class InitializeResult(Result):
     """The version of the Model Context Protocol that the server wants to use."""
     capabilities: ServerCapabilities
     serverInfo: Implementation
+    instructions: str | None = None
+    """Instructions describing how to use the server and its features."""
 
 
 class InitializedNotification(Notification):
diff --git a/tests/client/test_session.py b/tests/client/test_session.py
index d15d16f..7de0473 100644
--- a/tests/client/test_session.py
+++ b/tests/client/test_session.py
@@ -51,6 +51,7 @@ async def test_client_session_initialize():
                     prompts=None,
                 ),
                 serverInfo=Implementation(name="mock-server", version="0.1.0"),
+                instructions="The server instructions."
             )
         )
 
@@ -92,6 +93,7 @@ async def test_client_session_initialize():
     assert result.protocolVersion == LATEST_PROTOCOL_VERSION
     assert isinstance(result.capabilities, ServerCapabilities)
     assert result.serverInfo == Implementation(name="mock-server", version="0.1.0")
+    assert result.instructions == "The server instructions."
 
     # Check that the client sent the initialized notification
     assert initialized_notification