diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0215cde..9816361 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,3 +24,4 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 - Update `HttpRequestUtil.request` documentation
 - Update license year
+- Add `X-Request-Id` header
diff --git a/src/utils/request.ts b/src/utils/request.ts
index 8ec180e..261a9b4 100644
--- a/src/utils/request.ts
+++ b/src/utils/request.ts
@@ -5,6 +5,8 @@
  * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/BSD-3-Clause
  */
 
+import { randomUUID } from "node:crypto";
+
 /** Error thrown by the SDK when receiving non-2xx responses on HTTP requests. */
 export class HTTPResponseError extends Error {
   response: any;
@@ -14,6 +16,13 @@ export class HTTPResponseError extends Error {
   }
 }
 
+/**
+ * UUID generator utility wrapping node:crypto's randomUUID for stubbing in tests
+ */
+export const uuidGenerator = {
+  generate: () => randomUUID(),
+};
+
 /**
  * Handles HTTP requests.
  */
@@ -23,7 +32,7 @@ export class HttpRequestUtil {
    * 
    * @param url - The URL to make the request to
    * @param opts - Fetch request options (method, headers, body, etc.). Headers will be merged 
-   *               with default headers `{ "User-Agent: heroku-applink-node-sdk/1.0" }`
+   *               with default User-Agent and X-Request-ID headers.
 
    * @param json - Whether to parse the response as JSON (default: true). If false, 
    *               returns the raw Response object
@@ -36,6 +45,7 @@ export class HttpRequestUtil {
       ...opts,
       headers: {
         "User-Agent": "heroku-applink-node-sdk/1.0",
+        "X-Request-Id": uuidGenerator.generate(),
         ...(opts?.headers ?? {}),
       },
     };
diff --git a/test/utils/request.test.ts b/test/utils/request.test.ts
index 11e3be9..9d94f02 100644
--- a/test/utils/request.test.ts
+++ b/test/utils/request.test.ts
@@ -7,15 +7,21 @@
 
 import { expect } from "chai";
 import sinon from "sinon";
-import { HttpRequestUtil, HTTPResponseError } from "../../src/utils/request";
+import {
+  HttpRequestUtil,
+  HTTPResponseError,
+  uuidGenerator,
+} from "../../src/utils/request";
 
 describe("HttpRequestUtil", () => {
   let httpRequestUtil: HttpRequestUtil;
   let fetchStub: sinon.SinonStub;
+  let uuidGeneratorStub: sinon.SinonStub;
 
   beforeEach(() => {
     httpRequestUtil = new HttpRequestUtil();
     fetchStub = sinon.stub(global, "fetch");
+    uuidGeneratorStub = sinon.stub(uuidGenerator, "generate");
   });
 
   afterEach(() => {
@@ -91,7 +97,54 @@ describe("HttpRequestUtil", () => {
       );
     });
 
+    it("should include default request-id header", async () => {
+      const mockUUID = "test-uuid-1234-5678-9abc";
+      uuidGeneratorStub.returns(mockUUID);
+
+      const mockResponse = {
+        ok: true,
+        status: 200,
+        statusText: "OK",
+        json: sinon.stub().resolves({}),
+      };
+      fetchStub.resolves(mockResponse);
+
+      await httpRequestUtil.request("https://api.example.com/test", {});
+
+      const [, options] = fetchStub.getCall(0).args;
+      expect(options.headers["X-Request-Id"]).to.equal(mockUUID);
+      expect(uuidGeneratorStub.calledOnce).to.be.true;
+    });
+
+    it("should generate unique request-id for each request", async () => {
+      const mockUUID1 = "test-uuid-1111-1111-1111";
+      const mockUUID2 = "test-uuid-2222-2222-2222";
+      uuidGeneratorStub.onFirstCall().returns(mockUUID1);
+      uuidGeneratorStub.onSecondCall().returns(mockUUID2);
+
+      const mockResponse = {
+        ok: true,
+        status: 200,
+        statusText: "OK",
+        json: sinon.stub().resolves({}),
+      };
+      fetchStub.resolves(mockResponse);
+
+      await httpRequestUtil.request("https://api.example.com/test1", {});
+      await httpRequestUtil.request("https://api.example.com/test2", {});
+
+      const [, options1] = fetchStub.getCall(0).args;
+      const [, options2] = fetchStub.getCall(1).args;
+
+      expect(options1.headers["X-Request-Id"]).to.equal(mockUUID1);
+      expect(options2.headers["X-Request-Id"]).to.equal(mockUUID2);
+      expect(uuidGeneratorStub.calledTwice).to.be.true;
+    });
+
     it("should merge custom headers with default headers", async () => {
+      const mockUUID = "test-uuid-merge-test";
+      uuidGeneratorStub.returns(mockUUID);
+
       const mockResponse = {
         ok: true,
         status: 200,
@@ -115,11 +168,15 @@ describe("HttpRequestUtil", () => {
       expect(options.headers["User-Agent"]).to.equal(
         "heroku-applink-node-sdk/1.0"
       );
+      expect(options.headers["X-Request-Id"]).to.equal(mockUUID);
       expect(options.headers["Content-Type"]).to.equal("application/json");
       expect(options.headers["Authorization"]).to.equal("Bearer token123");
     });
 
     it("should allow custom headers to override User-Agent", async () => {
+      const mockUUID = "test-uuid-override-test";
+      uuidGeneratorStub.returns(mockUUID);
+
       const mockResponse = {
         ok: true,
         status: 200,
@@ -138,6 +195,37 @@ describe("HttpRequestUtil", () => {
 
       const [, options] = fetchStub.getCall(0).args;
       expect(options.headers["User-Agent"]).to.equal("custom-agent/1.0");
+      expect(options.headers["X-Request-Id"]).to.equal(mockUUID);
+    });
+
+    it("should allow custom headers to override request-id", async () => {
+      // UUID generator should still be called since it's called before merging custom headers
+      uuidGeneratorStub.returns("generated-uuid-that-gets-overridden");
+
+      const mockResponse = {
+        ok: true,
+        status: 200,
+        statusText: "OK",
+        json: sinon.stub().resolves({}),
+      };
+      fetchStub.resolves(mockResponse);
+
+      const customRequestId = "custom-request-id-123";
+      const customOpts = {
+        headers: {
+          "X-Request-Id": customRequestId,
+        },
+      };
+
+      await httpRequestUtil.request("https://api.example.com/test", customOpts);
+
+      const [, options] = fetchStub.getCall(0).args;
+      expect(options.headers["X-Request-Id"]).to.equal(customRequestId);
+      expect(options.headers["User-Agent"]).to.equal(
+        "heroku-applink-node-sdk/1.0"
+      );
+      // UUID generator should still be called since it's called before merging custom headers
+      expect(uuidGeneratorStub.calledOnce).to.be.true;
     });
 
     it("should throw HTTPResponseError for 4xx status codes", async () => {