The course is structured in two blocks. The first one introduces the United Nations, its goals, its main bodies and its decision-making process as a starting point. It then focuses on the UN architecture as a decisive international actor regarding international peace and security by analyzing: the UN institutional framework that deals with these issues (the UN Security Council, the Department of Peacekeeping Operations, the Department of Political Affairs, etc.); relevant aspects of the UN Charter in relation to this topic (Chapters VI and VII); and the historical evolution of how the UN has coped with peace and security issues. The second block explores one of the main tools the United Nations applies to maintain peace and security: the UN Peace Operations. This is done by focusing on theoretical debates that have shaped the missions over the time, by examining their evolution in nature and scope and by grasping historical examples (Sierra Leone, Haiti, Burundi, Timor-Leste, Afghanistan, etc...).