This book presents the findings of a Joint Presidential Task Force of the Society of Clinical Psychology (Division 12 of APA) and of the North American Society for Psychotherapy Research. This task force was charged with integrating two previous task force findings which addressed, respectively, Treatments That Work (Division 12, APA), and Relationships That Work (Division 29, APA). This book transcends particular models of psychotherapy and treatment techniques to define treatments in terms of cross-cutting principles of therapeutic change. It also integrates relationship and participant factors with treatment techniques and procedures, giving special attention to the empirical grounding of multiple contributors to change. The result is a series of over 60 principles for applying treatments to four problem areas: depression, anxiety disorders, personality disorders, and substance abuse disorders. This book explains both principles that are common to many problem areas and those that are specific to different populations in a format that is designed to help the clinician optimize treatment planning.