Over the last twenty years, historical sociology has become an increasingly conspicuous part of the broader field of International Relations (IR) theory, with advocates making a series of interventions in subjects as diverse as the origins and varieties of international systems over time and place, to work on the co-constitutive relationship between the international realm and state-society relations in processes of radical change. However, even as historical sociology in IR (HSIR) has produced substantial gains, so there has also been a concomitant watering down of the underlying approach itself. As a result, it is no longer clear what exactly HSIR entails: should it be seen as operating within the existing pool of available theories or as an attempt to reconvene the discipline on new foundations? This article sets out an identifiable set of assumptions and precepts for HSIR based on deep ontological realism, epistemological relationism, a methodological free range, and an overt normative engagement with the events and processes that make up contemporary world politics. As such, HSIR can be seen as operating as an open society, a research programme and a vocation. Every field of enquiry goes through an important and necessary stage during which scholars turn their attention to the kind of enterprise in which they are engaged. After a prolonged period of concern with substantive matters, self-consciousness of purpose develops and questions arise about the road that has been travelled to date and the direction which enquiry should follow in the future. At this point, histories of the field are written, exploration of its boundaries are undertaken, methods of research are sensitized, and the requirements of further theoretical concepts are re-examined.While it is not clear whether this process of maturation constitutes "healthy fervent" or "hopeless confusion", the nature and limits of the field eventually emerge with greater clarity, thus enabling its practitioners to move on to the central task of accumulating knowledge through the investigation and interpretation of substantive materials.This article is a Rosenau-inspired stock-taking exercise into the use of historical sociology in International Relations (HSIR). Neither the broader enterprise of historical sociology nor the more particular orientations of HSIR are, of course, the FPA's of their day. Historical sociology can be seen as at least two-centuries old (albeit depending to some extent on when and where you start counting) -an attempt by economists, philosophers of history and nascent sociologists to provide a historically sensitive, yet generally applicable, account of the emergence of capitalism, industrialisation, rationalism, bureaucratisation, urbanisation (Rosenberg 1994a(Rosenberg , 2006. HSIR is now a formally recognised, if still minority, approach within the discipline.In which case, why the need for a stock-take? The answer is hinted at by Rosenau (1969: 1): 'After a prolonged period of concern with substantive matters, self-consci...