This review describes the contribution of psychiatric epidemiology to our understanding of the distribution and determinants of psychiatric disorders. First, it describes basic concepts within epidemiology, such as prevalence, incidence, case definition, bias, and confounding, and their specific meaning within psychiatric research. The two basic study designs in epidemiology, cohort and case-control, are then reviewed. This discussion includes a tutorial on how to calculate key measures of association: risk ratio and odds ratio. Major community-based studies in psychiatric epidemiology are then reviewed, focusing on the Epidemiologic Catchment Area Study, the National Comorbidity Study and the National Comorbidity Study Replication, the National Survey of American Life, the National Latino and Asian American Study of Mental Health, and the National Epidemiologic Survey on Alcohol and Related Conditions. The review concludes with a discussion of pharmacoepidemiology and how it is critical to our understanding of the full impact of psychiatric medications postmarketing. In the future, epidemiology will be revolutionized with “big data” collection in both institutional and community settings. Nonetheless, the basic concepts presented in this review will continue to be relevant and critical to drawing sound, evidence-based conclusions about the true nature, correlates, and causes of psychiatric disorders. This review contains 6 tables, and 63 references. Key words: case-control study, cohort study, community-based studies, measures of association, pharmacoepidemiology, psychiatric epidemiology