The chapter reviews the literature on the political economy of international organizations (IOs). Considering IOs as products of the preferences of various actors rather than monolithic entities, the authors focus on national politicians, international bureaucrats, interest groups, and voters. By looking into the details of decision-making in IOs, the literature shows that a focus on states as the prime actors in IOs overlooks important facets of the empirical reality. Mainly focusing on empirical research, the authors discuss the four main actors involved and examine how they influence, use, and shape IOs. They find that IO behavior often reflects the interests of politicians, bureaucrats, and interest groups, while the impact of voters is limited. The final section reviews proposals for reforms addressing this weak representation of voter preferences.