Epidemiology is the study of the distribution of disease and its determinants in human populations. Epidemiology usually takes place in an applied public health context. It focuses on the occurrence of disease by time, place, and person and seeks to identify and control outbreaks of disease through identification of etiological factors. Its approach is to identify associated risk factors and then work back to causes.

Historically, the focus of epidemiology was on large outbreaks, usually of infectious disease. The substance and methods of epidemiology have been applied to most forms of acute and chronic disease and many other physical and mental health conditions. Along with the broadening of the subject matter of epidemiology has come more focus on its methods. Along with the specialization of epidemiological methods has come the professional identification of persons as epidemiologists. In this entry, we address the origins, methodology, current topics, and professional...