This ground-breaking volume, published by the American Psychological Association in partnership with the International Union of Psychological Science, provides a detailed guide for the clinical implementation of the ICD-11 diagnostic classification system by psychologists and other health professionals. The World Health Assembly adopted the Eleventh Revision of the International Classification of Diseases (ICD-11) in 2019 as the basis for global health information and reporting. This edited volume offers a step-by-step approach to diagnosis, giving psychologists and trainees around the world the tools they need to apply ICD-11 diagnostic requirements for mental, behavioral, and neurodevelopmental disorders as the basis for delivering high quality, evidence-informed care. Authors summarize impairment, functioning, assessment, the developmental approach, terminology, research methodologies, and other key aspects of psychological practice. Each chapter describes a psychological approach to a different diagnostic area, operationalized as a conceptually driven, person-oriented, biopsychosociocultural formulation that integrates pertinent history, behavior, symptoms, phenomenology, and functioning. Written to be responsive to the unique context of psychological practice, including consideration of regional, linguistic, and cultural factors, A Psychological Approach to Diagnosis is the first comprehensive training resource on WHO’s ICD-11 classification of mental, behavioral and neurodevelopmental disorders. This book is designed to complement the World Health Organization’s Clinical Descriptions and Diagnostic Requirements (CDDR) for ICD-11 Mental, Behavioural and Neurodevelopmental Disorders.