This chapter reviews the basic elements of research methodology that characterize applied medical anthropology in the area of primary health care, using studies of diarrhea as the basis for discussion. It discusses the kinds of theoretical approaches current in one sector of medical anthropology, and examines main elements of methodology used in recent anthropological research on diarrhea and similar areas of investigation. Many research projects in medical anthropology are designed to focus on particular illnesses or pathological conditions, which are conceptualized as the dependent variables, to be predicted or “explained” by multiple independent variables. Anthropological research from diverse cultures shows that most cultural groups recognize several different varieties of childhood diarrhea, as the following examples illustrate. In community health research it has been productive to devote considerable attention to observed and reported behaviors, even when part of the design calls for delineation of “cognitive maps” concerning diarrheal illness and treatment.