This paper describes the theory of the actor-network, a body of theoretical and empirical writing which treats social relations, including power and organization, as network effects. The theory is distinctive because it insists that networks are materially heterogeneous and argues that society and organization would not exist if they were simply social. Agents, texts, devices, architectures are all generated in, form part of, and are essential to, the networks of the social. And in the first instance, all should be analyzed in the same terms. Accordingly, in this view, the task of sociology is to characterize the ways in which materials join together to generate themselves and reproduce institutional and organizational patterns in the networks of the social.