This groundbreaking core textbook offers a comprehensive overview of different approaches to the assessment and treatment of psychological disorders. The book retains important diagnostic perspectives, including the DSM-5, ICD-10, ICD-11 and PDM, but also widens the scope of coverage beyond mainstream psychiatric models to include psychological, biological, historical, sociocultural and therapeutic approaches. Contemporary and well-balanced, this book provides an even-handed and holistic foundation, allowing students to develop a strong critical mindset while retaining a robust research-driven orientation. This book is ideal for undergraduate and postgraduates students on abnormal psychology, psychopathology, mental health or clinical psychology modules.