Societies embarked on the fragile transition from war to peace face enormous economic, social, and political challenges. In attempting to support this transition, the international community often provides substantial amounts of external assistance. This aid can play an important and constructive role in meeting pressing social needs and building a durable peace, but it would be naïve to assume either that positive effects are the automatic result of good intentions or that donors are motivated entirely by the objective of peacebuilding. This paper reviews evidence on the impact of aid in “post-conflict” settings and offers suggestions for making aid more effective in supporting efforts to build a durable peace. Part I discusses how economic assistance and conditionalities can be realigned to better serve peacebuilding objectives. Part II considers the other side of the coin: how peacekeeping operations and peacebuilding assistance can better support economic recovery, in particular by helping to build state fiscal capacities. Finally, Part III examines the interests and incentive structures that shape the behavior of aid donors, suggesting that their actions can be part of the problem as well as part of the solution.