When, why, and how do countries move from hostile to peaceful relations, and sometimes even friendship? We draw on the interstate peace literature to identify two peace processes. Rapprochement represents a first step during which enemies might develop normal working relations. Some states then progress to conciliation and establish warm and cooperative ties. We compare rapprochement to conciliation, outline the mechanisms that drive each process, and review scholarly findings about three types of causal variables: abrupt shocks, stable contextual factors, and policy initiatives. A key insight emerges that conciliation is not simply an extension of rapprochement—the predictors of these two processes differ significantly. We then call for greater scholarly attention to the study of conciliation, interactions of causal factors, the domestic politics underlying each process, the causes of peace failure, and empirical and methodological challenges.