diff --git a/spec/operators/groupBy-spec.ts b/spec/operators/groupBy-spec.ts
index 6e4adf2771..6f1eb8bdae 100644
--- a/spec/operators/groupBy-spec.ts
+++ b/spec/operators/groupBy-spec.ts
@@ -1,6 +1,6 @@
 import {expect} from 'chai';
 import * as Rx from '../../dist/cjs/Rx';
-import {GroupedObservable} from '../../dist/cjs/operator/groupBy';
+import {GroupedObservable} from '../../dist/cjs/operators/groupBy';
 import marbleTestingSignature = require('../helpers/marble-testing'); // tslint:disable-line:no-require-imports
 
 declare const { asDiagram };
diff --git a/src/operator/groupBy.ts b/src/operator/groupBy.ts
index de801caf17..9ceb6fe34f 100644
--- a/src/operator/groupBy.ts
+++ b/src/operator/groupBy.ts
@@ -1,10 +1,7 @@
-import { Subscriber } from '../Subscriber';
-import { Subscription } from '../Subscription';
+
 import { Observable } from '../Observable';
-import { Operator } from '../Operator';
 import { Subject } from '../Subject';
-import { Map } from '../util/Map';
-import { FastMap } from '../util/FastMap';
+import { groupBy as higherOrder, GroupedObservable } from '../operators/groupBy';
 
 /* tslint:disable:max-line-length */
 export function groupBy<T, K>(this: Observable<T>, keySelector: (value: T) => K): Observable<GroupedObservable<K, T>>;
@@ -84,210 +81,5 @@ export function groupBy<T, K, R>(this: Observable<T>, keySelector: (value: T) =>
                                  elementSelector?: ((value: T) => R) | void,
                                  durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>,
                                  subjectSelector?: () => Subject<R>): Observable<GroupedObservable<K, R>> {
-  return this.lift(new GroupByOperator(keySelector, elementSelector, durationSelector, subjectSelector));
-}
-
-export interface RefCountSubscription {
-  count: number;
-  unsubscribe: () => void;
-  closed: boolean;
-  attemptedToUnsubscribe: boolean;
-}
-
-class GroupByOperator<T, K, R> implements Operator<T, GroupedObservable<K, R>> {
-  constructor(private keySelector: (value: T) => K,
-              private elementSelector?: ((value: T) => R) | void,
-              private durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>,
-              private subjectSelector?: () => Subject<R>) {
-  }
-
-  call(subscriber: Subscriber<GroupedObservable<K, R>>, source: any): any {
-    return source.subscribe(new GroupBySubscriber(
-      subscriber, this.keySelector, this.elementSelector, this.durationSelector, this.subjectSelector
-    ));
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class GroupBySubscriber<T, K, R> extends Subscriber<T> implements RefCountSubscription {
-  private groups: Map<K, Subject<T|R>> = null;
-  public attemptedToUnsubscribe: boolean = false;
-  public count: number = 0;
-
-  constructor(destination: Subscriber<GroupedObservable<K, R>>,
-              private keySelector: (value: T) => K,
-              private elementSelector?: ((value: T) => R) | void,
-              private durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>,
-              private subjectSelector?: () => Subject<R>) {
-    super(destination);
-  }
-
-  protected _next(value: T): void {
-    let key: K;
-    try {
-      key = this.keySelector(value);
-    } catch (err) {
-      this.error(err);
-      return;
-    }
-
-    this._group(value, key);
-  }
-
-  private _group(value: T, key: K) {
-    let groups = this.groups;
-
-    if (!groups) {
-      groups = this.groups = typeof key === 'string' ? new FastMap() : new Map();
-    }
-
-    let group = groups.get(key);
-
-    let element: R;
-    if (this.elementSelector) {
-      try {
-        element = this.elementSelector(value);
-      } catch (err) {
-        this.error(err);
-      }
-    } else {
-      element = <any>value;
-    }
-
-    if (!group) {
-      group = this.subjectSelector ? this.subjectSelector() : new Subject<R>();
-      groups.set(key, group);
-      const groupedObservable = new GroupedObservable(key, group, this);
-      this.destination.next(groupedObservable);
-      if (this.durationSelector) {
-        let duration: any;
-        try {
-          duration = this.durationSelector(new GroupedObservable<K, R>(key, <Subject<R>>group));
-        } catch (err) {
-          this.error(err);
-          return;
-        }
-        this.add(duration.subscribe(new GroupDurationSubscriber(key, group, this)));
-      }
-    }
-
-    if (!group.closed) {
-      group.next(element);
-    }
-  }
-
-  protected _error(err: any): void {
-    const groups = this.groups;
-    if (groups) {
-      groups.forEach((group, key) => {
-        group.error(err);
-      });
-
-      groups.clear();
-    }
-    this.destination.error(err);
-  }
-
-  protected _complete(): void {
-    const groups = this.groups;
-    if (groups) {
-      groups.forEach((group, key) => {
-        group.complete();
-      });
-
-      groups.clear();
-    }
-    this.destination.complete();
-  }
-
-  removeGroup(key: K): void {
-    this.groups.delete(key);
-  }
-
-  unsubscribe() {
-    if (!this.closed) {
-      this.attemptedToUnsubscribe = true;
-      if (this.count === 0) {
-        super.unsubscribe();
-      }
-    }
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class GroupDurationSubscriber<K, T> extends Subscriber<T> {
-  constructor(private key: K,
-              private group: Subject<T>,
-              private parent: GroupBySubscriber<any, K, T>) {
-    super(group);
-  }
-
-  protected _next(value: T): void {
-    this.complete();
-  }
-
-  protected _unsubscribe() {
-    const { parent, key } = this;
-    this.key = this.parent = null;
-    if (parent) {
-      parent.removeGroup(key);
-    }
-  }
-}
-
-/**
- * An Observable representing values belonging to the same group represented by
- * a common key. The values emitted by a GroupedObservable come from the source
- * Observable. The common key is available as the field `key` on a
- * GroupedObservable instance.
- *
- * @class GroupedObservable<K, T>
- */
-export class GroupedObservable<K, T> extends Observable<T> {
-  constructor(public key: K,
-              private groupSubject: Subject<T>,
-              private refCountSubscription?: RefCountSubscription) {
-    super();
-  }
-
-  protected _subscribe(subscriber: Subscriber<T>) {
-    const subscription = new Subscription();
-    const {refCountSubscription, groupSubject} = this;
-    if (refCountSubscription && !refCountSubscription.closed) {
-      subscription.add(new InnerRefCountSubscription(refCountSubscription));
-    }
-    subscription.add(groupSubject.subscribe(subscriber));
-    return subscription;
-  }
-}
-
-/**
- * We need this JSDoc comment for affecting ESDoc.
- * @ignore
- * @extends {Ignored}
- */
-class InnerRefCountSubscription extends Subscription {
-  constructor(private parent: RefCountSubscription) {
-    super();
-    parent.count++;
-  }
-
-  unsubscribe() {
-    const parent = this.parent;
-    if (!parent.closed && !this.closed) {
-      super.unsubscribe();
-      parent.count -= 1;
-      if (parent.count === 0 && parent.attemptedToUnsubscribe) {
-        parent.unsubscribe();
-      }
-    }
-  }
+  return higherOrder(keySelector, elementSelector as any, durationSelector, subjectSelector)(this);
 }
diff --git a/src/operators/groupBy.ts b/src/operators/groupBy.ts
new file mode 100644
index 0000000000..3ed28a6966
--- /dev/null
+++ b/src/operators/groupBy.ts
@@ -0,0 +1,295 @@
+import { Subscriber } from '../Subscriber';
+import { Subscription } from '../Subscription';
+import { Observable } from '../Observable';
+import { Operator } from '../Operator';
+import { Subject } from '../Subject';
+import { Map } from '../util/Map';
+import { FastMap } from '../util/FastMap';
+import { OperatorFunction } from '../interfaces';
+
+/* tslint:disable:max-line-length */
+export function groupBy<T, K>(keySelector: (value: T) => K): OperatorFunction<T, GroupedObservable<K, T>>;
+export function groupBy<T, K>(keySelector: (value: T) => K, elementSelector: void, durationSelector: (grouped: GroupedObservable<K, T>) => Observable<any>): OperatorFunction<T, GroupedObservable<K, T>>;
+export function groupBy<T, K, R>(keySelector: (value: T) => K, elementSelector?: (value: T) => R, durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>): OperatorFunction<T, GroupedObservable<K, R>>;
+export function groupBy<T, K, R>(keySelector: (value: T) => K, elementSelector?: (value: T) => R, durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>, subjectSelector?: () => Subject<R>): OperatorFunction<T, GroupedObservable<K, R>>;
+/* tslint:enable:max-line-length */
+
+/**
+ * Groups the items emitted by an Observable according to a specified criterion,
+ * and emits these grouped items as `GroupedObservables`, one
+ * {@link GroupedObservable} per group.
+ *
+ * <img src="./img/groupBy.png" width="100%">
+ *
+ * @example <caption>Group objects by id and return as array</caption>
+ * Observable.of<Obj>({id: 1, name: 'aze1'},
+ *                    {id: 2, name: 'sf2'},
+ *                    {id: 2, name: 'dg2'},
+ *                    {id: 1, name: 'erg1'},
+ *                    {id: 1, name: 'df1'},
+ *                    {id: 2, name: 'sfqfb2'},
+ *                    {id: 3, name: 'qfs3'},
+ *                    {id: 2, name: 'qsgqsfg2'}
+ *     )
+ *     .groupBy(p => p.id)
+ *     .flatMap( (group$) => group$.reduce((acc, cur) => [...acc, cur], []))
+ *     .subscribe(p => console.log(p));
+ *
+ * // displays:
+ * // [ { id: 1, name: 'aze1' },
+ * //   { id: 1, name: 'erg1' },
+ * //   { id: 1, name: 'df1' } ]
+ * //
+ * // [ { id: 2, name: 'sf2' },
+ * //   { id: 2, name: 'dg2' },
+ * //   { id: 2, name: 'sfqfb2' },
+ * //   { id: 2, name: 'qsgqsfg2' } ]
+ * //
+ * // [ { id: 3, name: 'qfs3' } ]
+ *
+ * @example <caption>Pivot data on the id field</caption>
+ * Observable.of<Obj>({id: 1, name: 'aze1'},
+ *                    {id: 2, name: 'sf2'},
+ *                    {id: 2, name: 'dg2'},
+ *                    {id: 1, name: 'erg1'},
+ *                    {id: 1, name: 'df1'},
+ *                    {id: 2, name: 'sfqfb2'},
+ *                    {id: 3, name: 'qfs1'},
+ *                    {id: 2, name: 'qsgqsfg2'}
+ *                   )
+ *     .groupBy(p => p.id, p => p.name)
+ *     .flatMap( (group$) => group$.reduce((acc, cur) => [...acc, cur], ["" + group$.key]))
+ *     .map(arr => ({'id': parseInt(arr[0]), 'values': arr.slice(1)}))
+ *     .subscribe(p => console.log(p));
+ *
+ * // displays:
+ * // { id: 1, values: [ 'aze1', 'erg1', 'df1' ] }
+ * // { id: 2, values: [ 'sf2', 'dg2', 'sfqfb2', 'qsgqsfg2' ] }
+ * // { id: 3, values: [ 'qfs1' ] }
+ *
+ * @param {function(value: T): K} keySelector A function that extracts the key
+ * for each item.
+ * @param {function(value: T): R} [elementSelector] A function that extracts the
+ * return element for each item.
+ * @param {function(grouped: GroupedObservable<K,R>): Observable<any>} [durationSelector]
+ * A function that returns an Observable to determine how long each group should
+ * exist.
+ * @return {Observable<GroupedObservable<K,R>>} An Observable that emits
+ * GroupedObservables, each of which corresponds to a unique key value and each
+ * of which emits those items from the source Observable that share that key
+ * value.
+ * @method groupBy
+ * @owner Observable
+ */
+export function groupBy<T, K, R>(keySelector: (value: T) => K,
+                                 elementSelector?: ((value: T) => R) | void,
+                                 durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>,
+                                 subjectSelector?: () => Subject<R>): OperatorFunction<T, GroupedObservable<K, R>> {
+  return (source: Observable<T>) =>
+    source.lift(new GroupByOperator(keySelector, elementSelector, durationSelector, subjectSelector));
+}
+
+export interface RefCountSubscription {
+  count: number;
+  unsubscribe: () => void;
+  closed: boolean;
+  attemptedToUnsubscribe: boolean;
+}
+
+class GroupByOperator<T, K, R> implements Operator<T, GroupedObservable<K, R>> {
+  constructor(private keySelector: (value: T) => K,
+              private elementSelector?: ((value: T) => R) | void,
+              private durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>,
+              private subjectSelector?: () => Subject<R>) {
+  }
+
+  call(subscriber: Subscriber<GroupedObservable<K, R>>, source: any): any {
+    return source.subscribe(new GroupBySubscriber(
+      subscriber, this.keySelector, this.elementSelector, this.durationSelector, this.subjectSelector
+    ));
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class GroupBySubscriber<T, K, R> extends Subscriber<T> implements RefCountSubscription {
+  private groups: Map<K, Subject<T|R>> = null;
+  public attemptedToUnsubscribe: boolean = false;
+  public count: number = 0;
+
+  constructor(destination: Subscriber<GroupedObservable<K, R>>,
+              private keySelector: (value: T) => K,
+              private elementSelector?: ((value: T) => R) | void,
+              private durationSelector?: (grouped: GroupedObservable<K, R>) => Observable<any>,
+              private subjectSelector?: () => Subject<R>) {
+    super(destination);
+  }
+
+  protected _next(value: T): void {
+    let key: K;
+    try {
+      key = this.keySelector(value);
+    } catch (err) {
+      this.error(err);
+      return;
+    }
+
+    this._group(value, key);
+  }
+
+  private _group(value: T, key: K) {
+    let groups = this.groups;
+
+    if (!groups) {
+      groups = this.groups = typeof key === 'string' ? new FastMap() : new Map();
+    }
+
+    let group = groups.get(key);
+
+    let element: R;
+    if (this.elementSelector) {
+      try {
+        element = this.elementSelector(value);
+      } catch (err) {
+        this.error(err);
+      }
+    } else {
+      element = <any>value;
+    }
+
+    if (!group) {
+      group = this.subjectSelector ? this.subjectSelector() : new Subject<R>();
+      groups.set(key, group);
+      const groupedObservable = new GroupedObservable(key, group, this);
+      this.destination.next(groupedObservable);
+      if (this.durationSelector) {
+        let duration: any;
+        try {
+          duration = this.durationSelector(new GroupedObservable<K, R>(key, <Subject<R>>group));
+        } catch (err) {
+          this.error(err);
+          return;
+        }
+        this.add(duration.subscribe(new GroupDurationSubscriber(key, group, this)));
+      }
+    }
+
+    if (!group.closed) {
+      group.next(element);
+    }
+  }
+
+  protected _error(err: any): void {
+    const groups = this.groups;
+    if (groups) {
+      groups.forEach((group, key) => {
+        group.error(err);
+      });
+
+      groups.clear();
+    }
+    this.destination.error(err);
+  }
+
+  protected _complete(): void {
+    const groups = this.groups;
+    if (groups) {
+      groups.forEach((group, key) => {
+        group.complete();
+      });
+
+      groups.clear();
+    }
+    this.destination.complete();
+  }
+
+  removeGroup(key: K): void {
+    this.groups.delete(key);
+  }
+
+  unsubscribe() {
+    if (!this.closed) {
+      this.attemptedToUnsubscribe = true;
+      if (this.count === 0) {
+        super.unsubscribe();
+      }
+    }
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class GroupDurationSubscriber<K, T> extends Subscriber<T> {
+  constructor(private key: K,
+              private group: Subject<T>,
+              private parent: GroupBySubscriber<any, K, T>) {
+    super(group);
+  }
+
+  protected _next(value: T): void {
+    this.complete();
+  }
+
+  protected _unsubscribe() {
+    const { parent, key } = this;
+    this.key = this.parent = null;
+    if (parent) {
+      parent.removeGroup(key);
+    }
+  }
+}
+
+/**
+ * An Observable representing values belonging to the same group represented by
+ * a common key. The values emitted by a GroupedObservable come from the source
+ * Observable. The common key is available as the field `key` on a
+ * GroupedObservable instance.
+ *
+ * @class GroupedObservable<K, T>
+ */
+export class GroupedObservable<K, T> extends Observable<T> {
+  constructor(public key: K,
+              private groupSubject: Subject<T>,
+              private refCountSubscription?: RefCountSubscription) {
+    super();
+  }
+
+  protected _subscribe(subscriber: Subscriber<T>) {
+    const subscription = new Subscription();
+    const {refCountSubscription, groupSubject} = this;
+    if (refCountSubscription && !refCountSubscription.closed) {
+      subscription.add(new InnerRefCountSubscription(refCountSubscription));
+    }
+    subscription.add(groupSubject.subscribe(subscriber));
+    return subscription;
+  }
+}
+
+/**
+ * We need this JSDoc comment for affecting ESDoc.
+ * @ignore
+ * @extends {Ignored}
+ */
+class InnerRefCountSubscription extends Subscription {
+  constructor(private parent: RefCountSubscription) {
+    super();
+    parent.count++;
+  }
+
+  unsubscribe() {
+    const parent = this.parent;
+    if (!parent.closed && !this.closed) {
+      super.unsubscribe();
+      parent.count -= 1;
+      if (parent.count === 0 && parent.attemptedToUnsubscribe) {
+        parent.unsubscribe();
+      }
+    }
+  }
+}
diff --git a/src/operators/index.ts b/src/operators/index.ts
index 2921296c4e..84dfabf597 100644
--- a/src/operators/index.ts
+++ b/src/operators/index.ts
@@ -29,6 +29,7 @@ export { finalize } from './finalize';
 export { find } from './find';
 export { findIndex } from './findIndex';
 export { first } from './first';
+export { groupBy } from './groupBy';
 export { ignoreElements } from './ignoreElements';
 export { map } from './map';
 export { materialize } from './materialize';