This document provides an introduction to Acceptance and Commitment Therapy (ACT). It discusses the principles and core processes of ACT including experiential avoidance, cognitive fusion, lack of contact with the present moment, inflexible sense of self, lack of values clarity, and lack of committed action. It provides examples of how ACT can help clients like Sue who struggles with depression, rumination, and suicidal thoughts. The document explains how ACT aims to increase psychological flexibility and build a more meaningful and fulfilling life through its six core therapeutic processes: acceptance, defusion, present moment awareness, self as observer, values clarification, and committed action.