International institutions are central features of modern international relations. This is true of trade, international debt and financial restructuring, and even national security, once the exclusive realm of pure state action. It was certainly true of the two major military engagements of the 1990s, the wars in Kosovo and the Persian Gulf. As international institutions have gained prominence in the political landscape, they have increasingly become prominent topics for study. The sharpest debate among researchers has been theoretical: Do international institutions really matter? Missing from this debate is a sustained inquiry into how these institutions actually work. We shift the focus by posing researchable questions about how they operate and how they relate to the problems states face.

We begin with a simple observation: major institutions are organized in radically different ways. Some are global, essentially open to all states; others are regional, with restricted memberships. Some institutions give each state an equal vote, whereas others have weighted voting and sometimes require supermajorities. Institutions may have relatively strong central authorities and significant operating responsibilities or be little more than forums for consultation. Some arrangements—for example, most bilateral treaties—have no formal organizational structure; these are plentiful because states have a striking tendency to codify their relationships in formal, legal arrangements.

Why do these differences exist? Do they really matter, both for members and for international politics more generally? Do they affect what the institutions themselves can do? We focus on these large questions of institutional design.