Much of social life involves interactions between individuals or corporate actors in dyads, groups, organizations or networks that can be viewed as social exchanges. This chapter presents an overview of the main theories of social exchange focusing on the key contributors in sociology, including George Homans, Peter Blau, Richard M. Emerson and those whose work subsequently built on their original formulations. The theories that have been developed in recent decades have focused on the social structures created by repeated exchanges and the ways in which these structures both constrain and enable actors to exercise power and influence. Other related social processes addressed within the exchange tradition include interpersonal commitment, trust, fairness, procedural and distributive justice, coalition formation and collective action. Recent work also focuses on emotions and their role in social exchange. The methodological challenges of studying social exchange in the laboratory and in the world outside the lab are addressed as well as links between exchange theory and topics under study by economic sociologists and network scholars more broadly, including Internet-mediated exchanges and their growing significance.