Introducing epidemiology as the study of health and illness in human populations, we discuss what questions modern epidemiology addresses, the key methods it uses, and how these methods can be applied to developmental psychopathology. A short history of how child psychiatric epidemiology has grown into developmental epidemiology illustrates society's changing concerns about child mental health. We describe some of the ways in which developmental epidemiology is branching out into related areas: life course and intergenerational epidemiology; global epidemiology; genetic epidemiology; the study of burden of disease, including cost‐benefit analysis; and the use of epidemiologic designs to test hypotheses about causation. Finally, we note that developmental epidemiology extends the range of translational epidemiology. We make the case that (1) the goal of epidemiological research is disease prevention; (2) understanding the development of a disease and intervening to prevent and control it are equally important aspects of epidemiological research; (3) understanding the development of a disease may point to different kinds of intervention at different stages in the developmental process; and (4) understanding individual development is a critical part of understanding and intervening in the disease process because both risk for and expression of disorder change over the life course.