With this much-needed introduction to the UN, Jussi Hanhimaki engages the current debate over the organizations effectiveness as he provides a clear understanding of how it was originally conceived, how it has come to its present form, and how it must confront new challenges in a rapidly changing world. After a brief history of the United Nations and its predecessor, the League of Nations, the author examines the UN's successes and failures as a guardian of international peace and security, as a promoter of human rights, as a protector of international law, and as an engineer of socio-economic development.