This book introduces the four principal sets of institutions that engage in bringing peace and relief to societies mired in violent conflicts and humanitarian crises—the United Nations and other international bodies; non-governmental organizations; civilian government agencies; and militaries. Because these institutions have distinct goals as well as overlapping mandates and activities on the ground, they do not always collaborate effectively, due in part to a lack of familiarity with how the other institutions are organized, make decisions or act on the ground. Despite declining public support for large-scale, state-building missions recently, more complex interagency efforts have evolved in partnership with host country governments. Numerous third parties continue to undertake peacebuilding, stabilization, and humanitarian relief measures around the globe. This book is intended primarily for those serving in the field, but it is also helpful to headquarters personnel and policymakers, as well as military and agency trainees and university students.