In this After Effects tutorial we'll learn how to key greenscreen or bluescreen footage in After Effects. Using greenscreens is a common practice in today's VFX workflow, so understanding how to get a good alpha from greenscreen footage is very important. We'll begin this tutorial by learning what a chroma key is and what we need to look out for while we shoot the greenscreen footage. From there, we begin keying a sample shot using the Keylight keyer. We'll then learn how to refine our matte and edge using the various built-in modifiers. Finally, we will composite our keyed footage over a background and learn about spill suppression and some compositing tricks to integrate our pieces of footage. We'll end the tutorial by learning a method of treating compressed or chroma subsampled footage to pull better keys. Software required: After Effects CS5 and up.