The Matrix is a simple method for teaching clients to understand the function of their behaviors (e.g., avoidance/escape versus moving toward values) as well as discriminate between events within and outside the skin (e.g., mental experiencing and direct experience). It was created by Kevin Polk, Mark Webster, and Jerold Hambright.
Here are links to three videos (on Youtube) that details the Matrix and demonstrates how to use it.
http://www.youtube.com/watch?
http://www.youtube.com/watch?
http://www.youtube.com/watch?
Attached to this page is a companion document that walks you through using it with clients.