This book presents essential background necessary for understanding the role of theory in psychotherapy practice, and shows how understanding psychotherapy theory is the first step to becoming an effective therapist. The author provides a thorough but concise overview of the history of psychotherapy, the evolution of psychotherapy theories, and research on the effectiveness of various psychotherapies in general practice and for treatment of specific common disorders. The book is an accessible, handy resource for students training to be psychotherapists and practitioners seeking to reevaluate theories and corresponding therapies. As the foundational book in the Theories of Psychotherapy Series, this title may be read first or in combination with other books in the series to establish a thorough understanding of psychotherapy and its variants. This updated second edition incorporates new developments in theory and research, new approaches including advances in culturally sensitive therapy, and updates in the classification of mental illness.