Among the many groups of scholars whose work now illuminates science, technology and medicine (STM), historians, it seems to me, have a key responsibility not just to elucidate change but to establish and explain variety. One of the big pictures we need is a model of the varieties of STM over time; one which does not presume the timeless existence of disciplines, or the distinctions between science, technology and medicine; a model which is both synchronic and diachronic, and both cognitive (...) and social. To that end, this brief paper presents a historical typology of STM from about 1700 to the present by focusing on four ‘ideal’ socio-cognitive types – four knowledge structures which correspond to four sets of social relations. To some extent these are period specific, but they do not have to be – hence, one may hope, the flexibility and usefulness of the model. (shrink)