Grounded in decades of influential research, this book thoroughly examines perfectionism: how it develops, its underlying mechanisms and psychological costs, and how to target it effectively in psychotherapy. The authors describe how perfectionistic tendencies--rooted in early relational and developmental experiences--make people vulnerable to a wide range of clinical problems. They present an integrative treatment approach and demonstrate ways to tailor interventions to the needs of individual clients. A group treatment model is also detailed. State-of-the-art assessment tools are discussed (and provided at the companion website). Throughout the book, vivid clinical illustrations make the core ideas and techniques concrete.