Is the acquisition of personnel for UN peacekeeping missions susceptible to free-riding by UN member states? If so, what drives this behavior and what impact does this have on obtaining required personnel for the mission? Using data from 21 missions in 13 African countries between 1990 and 2010, this article addresses whether UN peacekeeping missions experience a shortfall in personnel due to incentives to free-ride by contributing states. It argues that as the number of states contributing to a mission increases, contributors have a greater incentive to free-ride and make suboptimal personnel contributions, leading to greater overall shortfall in the mission’s personnel. However, this free-riding behavior can be mitigated by the economic incentives of contributor states. The findings support two central tenets of collective action theory: that free-riding by member states contributing to the mission is more prevalent when the number of contributors is larger, and when selective incentives such as economic gains are lower. These findings have implications for the strategic composition and efficacy of peacekeeping forces. More broadly, the results underscore the struggle of international organizations to obtain compliance from member states in achieving their international objectives.