States are expected to provide both security and justice for their citizens; one needs the other in order to work well. Yet when both are damaged or destroyed by war, state actors and outsiders alike tend to treat them as competing post-conflict priorities. Over the past twenty years, numerous processes have emerged to promote one or both, including “transitional justice”—from courts and truth commissions to community reconciliation—and programs to restore rule of law, reform the “security sector” (SSR) and disarm, demobilize, and reintegrate fighters into society (DDR). The many actors involved have just as many, sometimes competing, operational priorities, knowing that change is urgent, but necessarily long-term. This chapter examines the interaction of transitional justice, rule of law, SSR, and DDR, identifying key concepts, actors, processes, and challenges in pursuing change in each of these areas simultaneously.