This article claims that the study of irregular migration may be a strategic research material for the development of an adequate understanding of contemporary society. The field, however, suffers not only from a lack of reliable empirical data, but also from endemic undertheorizing. The article shows how the attempt to develop an understanding of irregular migration from within a general theory of modern society has positive consequences both for the clarification of the problems and for the design of research programs (...) able to deal adequately with the phenomena. Particularly, it is argued that a theory of modern society centered on its form of differentiation may help to clarify both the political dimension of contemporary international mobility, the variety of irregular statuses existing in the foreign population of receiving countries, and the condition of inclusion and exclusion of irregular migrants. (shrink)