This chapter assesses the contributions of British UN staff to global security, peacekeeping, and civilian aid initiatives. The UN’s conflict and security work attracted much public attention between 1945 and 1970. While it achieved mixed success in mediating postwar global crises in Palestine, Kashmir, Korea, Egypt, and Congo, its missions performed important regional security work at the local level. UN operations in South Kasai during the Congo Crisis in the early 1960s are used as a case study. UN civil servants also provided security through technical governance and state-building initiatives. The chapter tracks this theme through studies of UN migration, population, and food projects; the relationship between UN development campaigns and late colonial planning paradigms; and British leadership in UN technical organizations.