The signing of a comprehensive peace agreement (CPA) is often seen as a historic milestone in a peace process, and its implementation takes a highly legitimized set of reforms and puts it front and center in national politics. This article examines the aggregate implementation of CPAs signed since 1989 and future conflict behavior between the negotiating parties and between the government and non-signatory groups. It argues that implementation is both a peace-building process and an outcome that normalizes political relations between hostile groups, solves commitment problems and addresses the root causes of civil conflict. Statistical tests utilizing new data on the implementation of CPAs support the argument. The extent to which an agreement is implemented is shown to have significant long-term effects on how long peace lasts – an effect that applies not only to the signatories of the agreement, but also to the government and non-signatory groups.