Although epidemiology as a scientific study of disease in populations claimed an independent disciplinary status already in the mid–nineteenth century, its history in the twentieth century can be seen as a continuous and often contentious attempt to define the field’s social and intellectual boundaries vis-à-vis a variety of neighboring scientific fields and public health practices. In a period dominated by laboratory biomedical sciences, epidemiologists repeatedly tried to spell out how their discipline met the requirements of scientificity despite its focus on (...) disease as a collective phenomenon and its reliance on nonlaboratory methods. This article asks about the relationship between the changing institutional and intellectual contexts of British epidemiological practice and the epidemiologists’attempts to define both science in general and epidemiology in particular. An examination of the epidemiologists’boundary-making endeavors is also used to reflect on the circumstances in which scientists engage in the discourse of disciplinary demarcations. (shrink)