This second edition of the APA Dictionary of Psychology®, part of the APA Reference Books Collection, is an authoritative and comprehensive resource designed for a wide audience, including psychologists, clinicians, students, professionals from allied mental health fields, and all interested readers. Featuring nearly 26,000 entries, it offers clear and definitive definitions, with approximately 1,000 more than the first edition. The dictionary provides balanced coverage across 90 subareas, with significant revisions and expansions in areas such as neuroscience, psychopharmacology, lifespan developmental psychology, statistics, experimental design, and many others. Thousands of incisive cross-references enhance understanding of related topics, while over 400 brief biographical entries on historical figures in psychology and other relevant fields offer additional insights, quadrupling the number from the first edition. The guide to the dictionary and a quick guide to format help users navigate its stylistic and structural features. Three appendixes—Institutional and Organizational Entries; Psychological Test and Assessment Instrument Entries; and Psychotherapeutic Techniques, Biological Treatments, and Related Entries—further enrich this indispensable reference tool.