Social theorists increasingly recognise that material things often play vital roles in the causation of social events. However there is substantial disagreement on how to theorise these roles. Several members of the Cambridge Social Ontology Group have made important contributions in the form of their work on the ontology of technological objects. This paper builds on their work to develop an ontology of socio-technical structures: social entities composed of both humans and technological objects, with causal powers that depend on how these parts relate to, and interact with, each other. The implication is that material things are not just significant in their own right, or as parts of technical complexes, but that they can play a central role in social structures themselves. Indeed many of the most important and consequential social structures in contemporary societies, and in particular in contemporary economies, are socio-technical structures
