How to Link Properties with Expressions in After Effects

Linking properties is one of the most powerful workflow techniques in After Effects. When you change one value, the linked value updates automatically.

Method 1: The Pick Whip (Easiest)
1. Alt/Option-click the stopwatch on the property you want to CONTROL (the follower)
2. Drag the spiral "pick whip" icon to the property you want to FOLLOW (the leader)
3. Release — AE writes the expression automatically

The resulting expression looks something like:

thisComp.layer("Circle").transform.position

Method 2: Manual Expression
Alt/Option-click the stopwatch and type:

thisComp.layer("Layer Name").transform.opacity

Replace "Layer Name" and the property path as needed.

Linking with math (the real power):

Direct link (1:1):

thisComp.layer("Control").transform.rotation

Inverse link:

-thisComp.layer("Control").transform.rotation

Scaled link (50% of the value):

thisComp.layer("Control").transform.rotation * 0.5

Offset link (add 90°):

thisComp.layer("Control").transform.rotation + 90

Linking between different property types:
Map position X to opacity:

linear(thisComp.layer("Box").transform.position[0], 0, 1920, 0, 100)

As the box moves from left (0) to right (1920), opacity goes from 0% to 100%.

Expression Controls (Pro technique):
For clean rigs, add Expression Controls (Effect → Expression Controls → Slider Control) to a null object. Then link everything to those sliders. This creates a "control panel" for your animation.

Pro tip: The pick whip is powerful, but understanding the expression syntax it generates will let you modify and extend links in ways the pick whip alone can't handle. After you pick-whip, read what it wrote — that's the best way to learn.