While the evolving nature and proliferation of UN peacekeeping operations in the post-Cold War period is well documented, we know less about how personnel are recruited for these missions. Furthermore, recent developments have rendered existing supply-side explanations for troop contributions less convincing. The increasing demand for personnel, along with stagnant UN reimbursement rates and the rising costs of participation that began during the 1990s, mean that it is less attractive than ever for developing countries to offer their own troops to what have become increasingly ambitious operations. Yet, we see a large pool of developing countries continuing to do so. To address this puzzle, we argue that UN member states with strong preferences for establishing peacekeeping missions have begun using foreign aid as an inducement to help potential contributors overcome the collective action problem inherent in multilateral peacekeeping operations. We uncover strong empirical evidence that these ‘pivotal states’ strategically allocate foreign aid to persuade contributing states to boost their contributions, and also to ensure that these missions continue to be staffed and maintained as costs rise, particularly during the post-1999 period. We also find that states are responsive to these financial inducements: foreign aid increases both the likelihood of contributing personnel and the size of a state’s contribution. Theoretically, this article advances the scholarly understanding of international organizations and cooperation by illuminating an informal, extra-organizational strategy by which IOs can facilitate cooperation.