In this paper, I argue for the development of explanatory theory in IS research. I critically examine ways of explaining IS phenomena, identify alternative epistemological approaches used in the social sciences, and point out the significance attributed to causality. I focus in particular on the development of explanation in process IS research that draws from social theory. I introduce the notion of social mechanism and suggest that tracing social mechanisms in research that draws from social theories of action and technology can lead to more complete and novel causal explanations of IS phenomena.