diff --git a/README.md b/README.md
index 3d9d99a..d1a7073 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,7 @@ Below is the list of all available errors:
 | ForbiddenError          | 403  | Forbidden             |
 | GoneError               | 410  | Gone                  |
 | NotFoundError           | 404  | Not Found             |
+| NotImplementedError     | 501  | Not Implemented
 | ServiceUnavailableError | 503  | Service Unavailable   |
 | TooManyRequestsError    | 429  | Too Many Requests     |
 | UnauthorizedError       | 401  | Unauthorized          |
diff --git a/src/errors/not-implemented-error.js b/src/errors/not-implemented-error.js
new file mode 100644
index 0000000..40f4e04
--- /dev/null
+++ b/src/errors/not-implemented-error.js
@@ -0,0 +1,21 @@
+'use strict';
+
+/**
+ * Module dependencies.
+ */
+
+const HttpError = require('./http-error');
+
+/**
+ * Export "Not Implemented" error.
+ */
+
+module.exports = class NotImplementedError extends HttpError {
+  /**
+   * Constructor.
+   */
+
+  constructor() {
+    super(501, ...arguments);
+  }
+};
diff --git a/src/index.js b/src/index.js
index 10e9f84..40b9bea 100644
--- a/src/index.js
+++ b/src/index.js
@@ -12,6 +12,7 @@ module.exports = {
   GoneError: require('./errors/gone-error'),
   HttpError: require('./errors/http-error'),
   NotFoundError: require('./errors/not-found-error'),
+  NotImplementedError: require('./errors/not-implemented-error'),
   ServiceUnavailableError: require('./errors/service-unavailable-error'),
   TooManyRequestsError: require('./errors/too-many-requests-error'),
   UnauthorizedError: require('./errors/unauthorized-error'),
diff --git a/test/errors/not-implemented-error_test.js b/test/errors/not-implemented-error_test.js
new file mode 100644
index 0000000..aef6889
--- /dev/null
+++ b/test/errors/not-implemented-error_test.js
@@ -0,0 +1,16 @@
+'use strict';
+
+/**
+ * Module dependencies.
+ */
+
+const { NotImplementedError } = require('../../src');
+const test = require('../utils/test-http-error');
+
+/**
+ * Test "Not Implemented" error.
+ */
+
+describe('NotImplementedError', () => {
+  test(NotImplementedError, 501, 'Not Implemented', false);
+});
diff --git a/types/errors/not-implemented-error.d.ts b/types/errors/not-implemented-error.d.ts
new file mode 100644
index 0000000..2fefcf6
--- /dev/null
+++ b/types/errors/not-implemented-error.d.ts
@@ -0,0 +1,5 @@
+import { HttpError } from './http-error';
+export declare class NotImplementedError extends HttpError {
+    constructor(message?: string, props?: object);
+    constructor(props?: object);
+}
diff --git a/types/index.d.ts b/types/index.d.ts
index 8dd55a8..7a0829f 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -5,6 +5,7 @@ export * from './errors/forbidden-error';
 export * from './errors/gone-error';
 export * from './errors/http-error';
 export * from './errors/not-found-error';
+export * from './errors/not-implemented-error';
 export * from './errors/service-unavailable-error';
 export * from './errors/too-many-requests-error';
 export * from './errors/unauthorized-error';