Why do countries comply with international agreements? How do international institutions influence states' compliance? These are central questions in international relations (IR) and arise naturally in many situations. One example is the following.

In the framework of the Long-Range Transboundary Air Pollution (LRTAP) Convention, twenty-one European countries agreed in 1985 to reduce their sulfur emissions by at least 30 percent, with 1980 as the base year. By the deadline for implementation in 1993, most countries had reported reaching this goal, and some reported much steeper reductions. This presents the characteristics of a classic collective action problem. Sulfur emission reduction entails large short-term costs. Furthermore, because acid rain travels over a long distance and often across borders, the potential benefits of emission reduction are widely diffused. The combination of concentrated costs and diffuse benefits may give rise to free-riding incentives. So it is natural to ask: why do countries comply with their commitments and how do international institutions influence national compliance?

According to a central argument in IR, international institutions can resolve such collective action problems among states: they monitor states' compliance with treaties and, by providing compliance information, they facilitate reciprocity and thus induce compliance.

Empirically, however, the monitoring program under the LRTAP Convention monitored only the aggregate pollution levels. It did not monitor or verify each country's emission reduction. Rather, for compliance measurement, the Convention essentially relied on governmental self-reports. Indeed, faced with collective action problems, many international institutions do not directly monitor states' compliance with treaties.