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.