This article sets out an account of the historical development and the contemporary elaboration of sociological approaches to constitutional law. It argues that recent years have seen a broad sociological turn in constitutional theory, such that sociological constitutionalism now forms a distinct field of legal research. This is due to the general increase in the importance of constitutionalism in different national societies across the globe. This is also due to the emergence of new patterns of constitutional formation, both within and beyond national societies, resulting from the interaction between national and domestic constitutional law. The article separates different constitutional-sociological approaches into two categories: those with a primarily national, and those with a primarily transnational focus. Overall, however, it claims that sociological constitutionalism is driven primarily by engagement with transnational law, and the main insights in this field relate, in different ways, to global p...