diff --git a/src/inMemory.test.ts b/src/inMemory.test.ts
new file mode 100644
index 00000000..f7e9e979
--- /dev/null
+++ b/src/inMemory.test.ts
@@ -0,0 +1,94 @@
+import { InMemoryTransport } from "./inMemory.js";
+import { JSONRPCMessage } from "./types.js";
+
+describe("InMemoryTransport", () => {
+  let clientTransport: InMemoryTransport;
+  let serverTransport: InMemoryTransport;
+
+  beforeEach(() => {
+    [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+  });
+
+  test("should create linked pair", () => {
+    expect(clientTransport).toBeDefined();
+    expect(serverTransport).toBeDefined();
+  });
+
+  test("should start without error", async () => {
+    await expect(clientTransport.start()).resolves.not.toThrow();
+    await expect(serverTransport.start()).resolves.not.toThrow();
+  });
+
+  test("should send message from client to server", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "test",
+      id: 1,
+    };
+
+    let receivedMessage: JSONRPCMessage | undefined;
+    serverTransport.onmessage = (msg) => {
+      receivedMessage = msg;
+    };
+
+    await clientTransport.send(message);
+    expect(receivedMessage).toEqual(message);
+  });
+
+  test("should send message from server to client", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "test",
+      id: 1,
+    };
+
+    let receivedMessage: JSONRPCMessage | undefined;
+    clientTransport.onmessage = (msg) => {
+      receivedMessage = msg;
+    };
+
+    await serverTransport.send(message);
+    expect(receivedMessage).toEqual(message);
+  });
+
+  test("should handle close", async () => {
+    let clientClosed = false;
+    let serverClosed = false;
+
+    clientTransport.onclose = () => {
+      clientClosed = true;
+    };
+
+    serverTransport.onclose = () => {
+      serverClosed = true;
+    };
+
+    await clientTransport.close();
+    expect(clientClosed).toBe(true);
+    expect(serverClosed).toBe(true);
+  });
+
+  test("should throw error when sending after close", async () => {
+    await clientTransport.close();
+    await expect(
+      clientTransport.send({ jsonrpc: "2.0", method: "test", id: 1 }),
+    ).rejects.toThrow("Not connected");
+  });
+
+  test("should queue messages sent before start", async () => {
+    const message: JSONRPCMessage = {
+      jsonrpc: "2.0",
+      method: "test",
+      id: 1,
+    };
+
+    let receivedMessage: JSONRPCMessage | undefined;
+    serverTransport.onmessage = (msg) => {
+      receivedMessage = msg;
+    };
+
+    await clientTransport.send(message);
+    await serverTransport.start();
+    expect(receivedMessage).toEqual(message);
+  });
+});
diff --git a/src/inMemory.ts b/src/inMemory.ts
new file mode 100644
index 00000000..2763f38c
--- /dev/null
+++ b/src/inMemory.ts
@@ -0,0 +1,54 @@
+import { Transport } from "./shared/transport.js";
+import { JSONRPCMessage } from "./types.js";
+
+/**
+ * In-memory transport for creating clients and servers that talk to each other within the same process.
+ */
+export class InMemoryTransport implements Transport {
+  private _otherTransport?: InMemoryTransport;
+  private _messageQueue: JSONRPCMessage[] = [];
+
+  onclose?: () => void;
+  onerror?: (error: Error) => void;
+  onmessage?: (message: JSONRPCMessage) => void;
+
+  /**
+   * Creates a pair of linked in-memory transports that can communicate with each other. One should be passed to a Client and one to a Server.
+   */
+  static createLinkedPair(): [InMemoryTransport, InMemoryTransport] {
+    const clientTransport = new InMemoryTransport();
+    const serverTransport = new InMemoryTransport();
+    clientTransport._otherTransport = serverTransport;
+    serverTransport._otherTransport = clientTransport;
+    return [clientTransport, serverTransport];
+  }
+
+  async start(): Promise<void> {
+    // Process any messages that were queued before start was called
+    while (this._messageQueue.length > 0) {
+      const message = this._messageQueue.shift();
+      if (message) {
+        this.onmessage?.(message);
+      }
+    }
+  }
+
+  async close(): Promise<void> {
+    const other = this._otherTransport;
+    this._otherTransport = undefined;
+    await other?.close();
+    this.onclose?.();
+  }
+
+  async send(message: JSONRPCMessage): Promise<void> {
+    if (!this._otherTransport) {
+      throw new Error("Not connected");
+    }
+
+    if (this._otherTransport.onmessage) {
+      this._otherTransport.onmessage(message);
+    } else {
+      this._otherTransport._messageQueue.push(message);
+    }
+  }
+}