Behavioral Activation (BA) is an innovative method for treating depression that belongs to the so-called "Third Wave" of cognitive-behavioral therapy. BA is based on the reinforcement loss theory of depression and posits that depression arises from stressful experiences and is maintained through avoidance behavior. The manual makes an important contribution to the further development of cognitive-behavioral therapy. Written in an understandable and practical manner, it includes a variety of application examples and clearly demonstrates the evolution of the method since Lewinsohn proposed the structure of pleasant activities.