Why are some civil wars settled peacefully and others violently? In this important work, Walter argues that successful peace agreements must do more than resolve the underlying issues between the factions. It is easier to get the parties to negotiate a settlement than to actually implement it. Credible guarantees of security and power sharing must be struck, and this outcome requires a third-party commitment during the treacherous and insecure period of demobilization and disarmament. Walter derives these insights by examining peace settlements of civil wars over the last 50 years. Although the costs of war, shifting power realities, and ethnic identity affect whether the parties seek a peaceful resolution, assurances that the combatants will not be attacked or exploited after signing the treaty remain key if agreements are to stick. The clear message to policymakers is that settling civil wars cannot be left to the combatants themselves. A trustworthy, deeply committed outside party is needed -- even if the warring groups have tired of war and agree on the terms of peace.