This monograph addresses the topic of ‘transitions’ in complex stability operations and is intended to serve a wide audience that includes military and civilian policymakers, international development experts, and scholars in academe. It is a primer, systematic review and comprehensive assessment of the fields of research and practice on transitions. Transitions are conceived of through four lenses: as a process, authority transfer, phasing, and end state. Considering these perspectives, the authors provide a definition of ‘transition’ in the context of complex stability operations. The intellectual landscape on transitions is immense. From a sample of more than 170 sources, the monograph outlines a typology of six transitional categories while noting their embedded interdependencies: war-to-peace, power, societal, political-democratic, security, and economic. The state of practice reveals a variety of “approaches” and “tools” to address the challenges of post-conflict transitions, although these tend to be narrow and serve parochial interests. The authors conclude with recommendations that include a need for greater research emphasis on the following: testing underlying assumptions of current transition tools and indicators, understanding institutional resilience, identifying thresholds and tipping points between transition phases, and isolating interdependencies between institutions experiencing simultaneous transitions.