This new edited volume offers a step-by-step approach to diagnosis, giving practicing psychologists and graduate trainees the essential information they need to apply the mental and behavioral diagnostic guidelines of the ICD-11 and deliver high quality, evidence-informed care around the world. Following the adoption of the Eleventh Revision of the International Classification of Diseases and Related Health Problems (ICD-11) in 2018, this volume is specifically based on a psychological approach to diagnosis: a conceptually driven, person-oriented formulation that integrates pertinent history, behavior, symptoms, phenomenology, and functioning. As laid out by the volume's expert contributors, the approach enables practitioners to establish a differential diagnosis using the ICD-11 as the principal classification framework. Each chapter discusses how psychologists conceive of diagnosis as well as focal consideration of impairment, functioning, assessment, the developmental approach, terminology, research methodologies, and other key aspects of psychological practice. 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 and behavioral disorders.