The current scale and scope of peacekeeping missions is unprecedented and with this increasing reliance on peacekeeping as a tool to manage threats to peace and security come questions about who should keep the peace. Is it, as many assume, the United Nations? Is it a regional organization, such as the African Union? Or is it an individual state? Each of these different types of peacekeeping operations have different strengths and weaknesses associated with them in terms of legitimacy, institutional capacity, local and regional awareness, resources, and military effectiveness. This dissertation analyzes types of peacekeeping operations to determine which is the most effective in restoring peace and stability and why. I use a structured, focused comparative case study methodology to examine eight cases of peacekeeping, across two countries, the Democratic Republic of Congo and Sierra Leone, each of which has been subject to all three types of peacekeeping operations. This approach allows me to hold a number of control variables constant, providing a clear test of the impact of the type of intervention. I found that the type of PKO makes a difference to the success or failure of that mission. PKOs run by lead states are more likely to be successful because they are more willing to use force and they are more likely to have the resources and capabilities necessary to implement that force. Further, I found that two types of PKOs working together can use their strengths to compensate for each other’s weaknesses. I also present a quantitative study with a larger sample size that both substantiates my findings and allows me to generalize them to a wider universe of cases. / Political Science