OBJECTIVE: To describe the Child and Adolescent Psychiatric Assessment (CAPA). The base interview covers the age range from 9 to 17 years. METHOD: The interview glossary that provides detailed operational definitions of symptoms and severity ratings is described, and psychometric data and further developments of the interview are presented. RESULTS: Across 5,962 parent-child interviews, the core sections of the CAPA (psychiatric symptoms, functional impairment, demographics, family structure and functioning) took on average 59 minutes for children and 66 minutes for parents. Test-retest reliability for diagnoses ranged from kappa = 0.55 for conduct disorder (CD) to kappa = 1.0 for substance abuse/dependence. Validity as judged by 10 different criteria was good. Developments of the CAPA include a shorter "gateway" version using core symptoms as screen items, a Spanish version, and versions for twin studies, use with young adults (YAPA), and preschool-age children (PAPA). CONCLUSIONS: There is a place in both research and clinical settings for a rigorously operationalized interview (such as the CAPA) that focuses on ensuring that respondents understand what is being asked and on clearly defining levels of symptom severity and functional impairment.