diff --git a/src/Scheduler.ts b/src/Scheduler.ts
index 00e8fa0739..e2477f4d0a 100644
--- a/src/Scheduler.ts
+++ b/src/Scheduler.ts
@@ -6,6 +6,6 @@ export interface Scheduler {
   schedule<T>(work: (state?: T) => Subscription | void, delay?: number, state?: T): Subscription;
   flush(): void;
   active: boolean;
-  actions: Action[];
+  actions: Action<any>[]; // XXX: use `any` to remove type param `T` from `Scheduler`.
   scheduledId: number;
 }
diff --git a/src/operator/bufferTime.ts b/src/operator/bufferTime.ts
index 6c3487ab2c..fed4bce35b 100644
--- a/src/operator/bufferTime.ts
+++ b/src/operator/bufferTime.ts
@@ -68,6 +68,13 @@ class BufferTimeOperator<T> implements Operator<T, T[]> {
   }
 }
 
+type CreationState<T> = {
+  bufferTimeSpan: number;
+  bufferCreationInterval: number,
+  subscriber: BufferTimeSubscriber<T>;
+  scheduler: Scheduler;
+};
+
 class BufferTimeSubscriber<T> extends Subscriber<T> {
   private buffers: Array<T[]> = [];
 
@@ -79,7 +86,7 @@ class BufferTimeSubscriber<T> extends Subscriber<T> {
     const buffer = this.openBuffer();
     if (bufferCreationInterval !== null && bufferCreationInterval >= 0) {
       const closeState = { subscriber: this, buffer };
-      const creationState = { bufferTimeSpan, bufferCreationInterval, subscriber: this, scheduler };
+      const creationState: CreationState<T> = { bufferTimeSpan, bufferCreationInterval, subscriber: this, scheduler };
       this.add(scheduler.schedule(dispatchBufferClose, bufferTimeSpan, closeState));
       this.add(scheduler.schedule(dispatchBufferCreation, bufferCreationInterval, creationState));
     } else {
@@ -140,10 +147,10 @@ function dispatchBufferTimeSpanOnly(state: any) {
   }
 }
 
-function dispatchBufferCreation(state: any) {
+function dispatchBufferCreation<T>(state: CreationState<T>) {
   const { bufferCreationInterval, bufferTimeSpan, subscriber, scheduler } = state;
   const buffer = subscriber.openBuffer();
-  const action = <Action>this;
+  const action = <Action<CreationState<T>>>this;
   if (!subscriber.isUnsubscribed) {
     action.add(scheduler.schedule(dispatchBufferClose, bufferTimeSpan, { subscriber, buffer }));
     action.schedule(state, bufferCreationInterval);
@@ -152,4 +159,4 @@ function dispatchBufferCreation(state: any) {
 
 function dispatchBufferClose({ subscriber, buffer }) {
   subscriber.closeBuffer(buffer);
-}
+}
\ No newline at end of file
diff --git a/src/operator/windowTime.ts b/src/operator/windowTime.ts
index 129ea7a378..7aa9bd5f0b 100644
--- a/src/operator/windowTime.ts
+++ b/src/operator/windowTime.ts
@@ -79,6 +79,13 @@ class WindowTimeOperator<T> implements Operator<T, Observable<T>> {
   }
 }
 
+type CreationState<T> = {
+  windowTimeSpan: number;
+  windowCreationInterval: number;
+  subscriber: WindowTimeSubscriber<T>;
+  scheduler: Scheduler;
+};
+
 class WindowTimeSubscriber<T> extends Subscriber<T> {
   private windows: Subject<T>[] = [];
 
@@ -90,7 +97,7 @@ class WindowTimeSubscriber<T> extends Subscriber<T> {
     if (windowCreationInterval !== null && windowCreationInterval >= 0) {
       let window = this.openWindow();
       const closeState = { subscriber: this, window, context: <any>null };
-      const creationState = { windowTimeSpan, windowCreationInterval, subscriber: this, scheduler };
+      const creationState: CreationState<T> = { windowTimeSpan, windowCreationInterval, subscriber: this, scheduler };
       this.add(scheduler.schedule(dispatchWindowClose, windowTimeSpan, closeState));
       this.add(scheduler.schedule(dispatchWindowCreation, windowCreationInterval, creationState));
     } else {
@@ -161,10 +168,10 @@ function dispatchWindowTimeSpanOnly<T>(state: TimeSpanOnlyState<T>) {
   (<any>this).schedule(state, windowTimeSpan);
 }
 
-function dispatchWindowCreation(state: any) {
+function dispatchWindowCreation<T>(state: CreationState<T>) {
   let { windowTimeSpan, subscriber, scheduler, windowCreationInterval } = state;
   let window = subscriber.openWindow();
-  let action = <Action>this;
+  let action = <Action<CreationState<T>>>this;
   let context = { action, subscription: <any>null };
   const timeSpanState = { subscriber, window, context };
   context.subscription = scheduler.schedule(dispatchWindowClose, windowTimeSpan, timeSpanState);
diff --git a/src/scheduler/Action.ts b/src/scheduler/Action.ts
index e434c7f29f..a294e76b87 100644
--- a/src/scheduler/Action.ts
+++ b/src/scheduler/Action.ts
@@ -1,11 +1,11 @@
 import {Subscription} from '../Subscription';
 import {Scheduler} from '../Scheduler';
 
-export interface Action extends Subscription {
-  work: (state?: any) => void|Subscription;
-  state?: any;
+export interface Action<T> extends Subscription {
+  work: (state?: T) => void|Subscription;
+  state?: T;
   delay?: number;
-  schedule(state?: any, delay?: number): void;
+  schedule(state?: T, delay?: number): void;
   execute(): void;
   scheduler: Scheduler;
   error: any;
diff --git a/src/scheduler/AnimationFrameAction.ts b/src/scheduler/AnimationFrameAction.ts
index 4a391e643f..f0c4a78405 100644
--- a/src/scheduler/AnimationFrameAction.ts
+++ b/src/scheduler/AnimationFrameAction.ts
@@ -4,7 +4,7 @@ import {AnimationFrame} from '../util/AnimationFrame';
 
 export class AnimationFrameAction<T> extends FutureAction<T> {
 
-  protected _schedule(state?: T, delay: number = 0): Action {
+  protected _schedule(state?: T, delay: number = 0): Action<T> {
     if (delay > 0) {
       return super._schedule(state, delay);
     }
diff --git a/src/scheduler/AnimationFrameScheduler.ts b/src/scheduler/AnimationFrameScheduler.ts
index 28beffd71c..5ca4a9ef40 100644
--- a/src/scheduler/AnimationFrameScheduler.ts
+++ b/src/scheduler/AnimationFrameScheduler.ts
@@ -4,7 +4,7 @@ import {QueueScheduler} from './QueueScheduler';
 import {AnimationFrameAction} from './AnimationFrameAction';
 
 export class AnimationFrameScheduler extends QueueScheduler {
-  scheduleNow<T>(work: (x?: T) => Subscription, state?: T): Action {
+  scheduleNow<T>(work: (x?: T) => Subscription, state?: T): Action<T> {
     return new AnimationFrameAction(this, work).schedule(state);
   }
 }
diff --git a/src/scheduler/AsapAction.ts b/src/scheduler/AsapAction.ts
index 85f2eb23bc..c08e43a660 100644
--- a/src/scheduler/AsapAction.ts
+++ b/src/scheduler/AsapAction.ts
@@ -4,7 +4,7 @@ import {FutureAction} from './FutureAction';
 
 export class AsapAction<T> extends FutureAction<T> {
 
-  protected _schedule(state?: T, delay: number = 0): Action {
+  protected _schedule(state?: T, delay: number = 0): Action<T> {
     if (delay > 0) {
       return super._schedule(state, delay);
     }
diff --git a/src/scheduler/AsapScheduler.ts b/src/scheduler/AsapScheduler.ts
index e829628c5c..b09bf286d4 100644
--- a/src/scheduler/AsapScheduler.ts
+++ b/src/scheduler/AsapScheduler.ts
@@ -4,7 +4,7 @@ import {Subscription} from '../Subscription';
 import {QueueScheduler} from './QueueScheduler';
 
 export class AsapScheduler extends QueueScheduler {
-  scheduleNow<T>(work: (x?: T) => Subscription, state?: T): Action {
+  scheduleNow<T>(work: (x?: T) => Subscription, state?: T): Action<T> {
     return new AsapAction(this, work).schedule(state);
   }
 }
diff --git a/src/scheduler/AsyncScheduler.ts b/src/scheduler/AsyncScheduler.ts
index a92a2a01c9..db5af54f55 100644
--- a/src/scheduler/AsyncScheduler.ts
+++ b/src/scheduler/AsyncScheduler.ts
@@ -4,7 +4,7 @@ import {Subscription} from '../Subscription';
 import {QueueScheduler} from './QueueScheduler';
 
 export class AsyncScheduler extends QueueScheduler {
-  scheduleNow<T>(work: (x?: any) => Subscription, state?: any): Action {
+  scheduleNow<T>(work: (x?: T) => Subscription, state?: T): Action<T> {
     return new FutureAction(this, work).schedule(state, 0);
   }
 }
diff --git a/src/scheduler/FutureAction.ts b/src/scheduler/FutureAction.ts
index 7cd21456d9..f340ee867f 100644
--- a/src/scheduler/FutureAction.ts
+++ b/src/scheduler/FutureAction.ts
@@ -3,7 +3,7 @@ import {Action} from './Action';
 import {Scheduler} from '../Scheduler';
 import {Subscription} from '../Subscription';
 
-export class FutureAction<T> extends Subscription implements Action {
+export class FutureAction<T> extends Subscription implements Action<T> {
 
   public id: number;
   public state: T;
@@ -30,14 +30,14 @@ export class FutureAction<T> extends Subscription implements Action {
     }
   }
 
-  schedule(state?: T, delay: number = 0): Action {
+  schedule(state?: T, delay: number = 0): Action<T> {
     if (this.isUnsubscribed) {
       return this;
     }
     return this._schedule(state, delay);
   }
 
-  protected _schedule(state?: T, delay: number = 0): Action {
+  protected _schedule(state?: T, delay: number = 0): Action<T> {
 
     // Always replace the current state with the new state.
     this.state = state;
diff --git a/src/scheduler/QueueAction.ts b/src/scheduler/QueueAction.ts
index bb89bb12f3..ee2a4cc287 100644
--- a/src/scheduler/QueueAction.ts
+++ b/src/scheduler/QueueAction.ts
@@ -2,7 +2,7 @@ import {Action} from './Action';
 import {FutureAction} from './FutureAction';
 
 export class QueueAction<T> extends FutureAction<T> {
-  protected _schedule(state?: T, delay: number = 0): Action {
+  protected _schedule(state?: T, delay: number = 0): Action<T> {
     if (delay > 0) {
       return super._schedule(state, delay);
     }
diff --git a/src/scheduler/QueueScheduler.ts b/src/scheduler/QueueScheduler.ts
index 97829015f3..84e4237159 100644
--- a/src/scheduler/QueueScheduler.ts
+++ b/src/scheduler/QueueScheduler.ts
@@ -6,7 +6,7 @@ import {Action} from './Action';
 
 export class QueueScheduler implements Scheduler {
   public active: boolean = false;
-  public actions: QueueAction<any>[] = [];
+  public actions: QueueAction<any>[] = []; // XXX: use `any` to remove type param `T` from `VirtualTimeScheduler`.
   public scheduledId: number = null;
 
   now() {
@@ -19,7 +19,8 @@ export class QueueScheduler implements Scheduler {
     }
     this.active = true;
     const actions = this.actions;
-    for (let action: QueueAction<any>; action = actions.shift(); ) {
+    // XXX: use `any` to remove type param `T` from `VirtualTimeScheduler`.
+    for (let action: QueueAction<any> = null; action = actions.shift(); ) {
       action.execute();
       if (action.error) {
         this.active = false;
@@ -35,11 +36,11 @@ export class QueueScheduler implements Scheduler {
       this.scheduleLater(work, delay, state);
   }
 
-  scheduleNow<T>(work: (x?: T) => Subscription | void, state?: T): Action {
+  scheduleNow<T>(work: (x?: T) => Subscription | void, state?: T): Action<T> {
     return new QueueAction(this, work).schedule(state);
   }
 
-  scheduleLater<T>(work: (x?: T) => Subscription | void, delay: number, state?: T): Action {
+  scheduleLater<T>(work: (x?: T) => Subscription | void, delay: number, state?: T): Action<T> {
     return new FutureAction(this, work).schedule(state, delay);
   }
 }
diff --git a/src/scheduler/VirtualTimeScheduler.ts b/src/scheduler/VirtualTimeScheduler.ts
index af0af7899a..b72a748a22 100644
--- a/src/scheduler/VirtualTimeScheduler.ts
+++ b/src/scheduler/VirtualTimeScheduler.ts
@@ -3,7 +3,7 @@ import {Subscription} from '../Subscription';
 import {Action} from './Action';
 
 export class VirtualTimeScheduler implements Scheduler {
-  actions: Action[] = [];
+  actions: Action<any>[] = []; // XXX: use `any` to remove type param `T` from `VirtualTimeScheduler`.
   active: boolean = false;
   scheduledId: number = null;
   index: number = 0;
@@ -38,8 +38,8 @@ export class VirtualTimeScheduler implements Scheduler {
     this.frame = 0;
   }
 
-  addAction<T>(action: Action) {
-    const actions = this.actions;
+  addAction<T>(action: Action<T>): void {
+    const actions: Action<T>[] = this.actions;
 
     actions.push(action);
 
@@ -66,7 +66,7 @@ export class VirtualTimeScheduler implements Scheduler {
   }
 }
 
-class VirtualAction<T> extends Subscription implements Action {
+class VirtualAction<T> extends Subscription implements Action<T> {
   state: T;
   delay: number;
   calls = 0;
@@ -83,7 +83,7 @@ class VirtualAction<T> extends Subscription implements Action {
       return this;
     }
     const scheduler = this.scheduler;
-    let action: Action;
+    let action: Action<T> = null;
     if (this.calls++ === 0) {
       // the action is not being rescheduled.
       action = this;