Why are international institutions organized in such different ways? Some, like the World Trade Organization (WTO) and the World Health Organization, seek very wide memberships. Others, like the Organization for Economic Cooperation and Development and the Group of Eight, are deliberately restricted. Some, like the UN, cover an extremely broad range of issues. Others are narrowly focused, dealing with a single product (Organization of Petroleum Exporting Countries, OPEC) or a single problem (Convention on International Trade in Endangered Species). Some, like the International Monetary Fund (IMF), perform a variety of centralized tasks and even negotiate sensitive economic policies with member states. Others do little more than organize meetings and collate information, as the Asia-Pacific Economic Cooperation forum does for its members. Most institutions allocate votes equally to all members. But a few of the more important institutions—including the IMF, European Union (EU), and UN Security Council—give large members more votes and effective veto power. Some institutions, like the Outer Space Treaty, are built around rigid promises. Others, like the WTO, allow states to alter their obligations when faced with unusual circumstances.

All these institutions address serious problems of international cooperation, but they are designed in very different ways to cope with them. What explains these differences in institutional design? The Rational Design project has one overriding aim: to make explicit the connections between specific cooperation problems and their institutional solutions.