Ecosocial theory is an emerging multilevel theory of disease distribution that seeks to integrate social and biologic reasoning, along with a dynamic, historical, and ecological perspective, to address population distributions of disease and social inequalities in health. Guided by the question, Who and what drives current and changing patterns of social inequalities in health?, its central focus is on how people literally embody—biologically—social conditions, thereby generating inequitable population distributions of health. Distinguishing features of ecosocial theory include its emphasis on (a) the importance of explicit theoretical frameworks for epidemiological and other public health research and (b) the accountability of public health scientists and practitioners for the frameworks, questions, and data they do—or do not—employ in their daily work. From an ecosocial perspective, theory is essential to epidemiological and other public research and practice for three reasons (Krieger, 2001a). First, as in any science, theory is what helps us structure our ...