This book provides a balanced and systematic overview of the UN's contributions and challenges, highlighting areas where it plays an essential role in global governance as well as areas of redundancy and needed reform. This book provides readers with a clear, well-organized reference resource to the entire UN system--its principal organs, specialized agencies, programs and funds, and key issues of engagement. Through individual entries, it examines the history of UN engagement, ranging from peace and security to migration and climate change. It moves beyond a simple description of UN entities as it assesses the development of ideas (such as that of sustainable development), as well as responses to changes in world politics. Finally, it presents both the significant successes of UN work and continued challenges. Meticulously researched, accessible entries written by two prominent UN scholars Entries on both successes and continued challenges of the UN system Primary source documents key to the founding of the UN