Acceptance and commitment therapy, or ACT (pronounced as a word rather than letters), is an emerging psychotherapeutic technique first developed into a complete system in the book Acceptance and Commitment Therapy by Steven Hayes, Kirk Strosahl, and Kelly Wilson. ACT marks what some call a third wave in behavior therapy. To understand what this means, it helps to know that the first wave refers to traditional behavior therapy, which works to replace harmful behaviors with constructive ones through a learning principle called conditioning. Cognitive therapy, the second wave of behavior thera