Can the international community help establish the rule of law in countries recovering from civil war? If so, how? This chapter develops a theory to explain how third parties like the UN can help rehabilitate state security and justice sector institutions at the national level, while simultaneously legitimizing those institutions in the eyes of citizens at the local level. The chapter provides illustrations of the theory at work, gleaned from the secondary literature and primary accounts of the successes and shortcomings of UN missions around the world. The UN is especially adept at combining carrots and sticks to encourage compliance with new rule of law standards, even in countries where the rule of law has never existed before. The theory stands in stark contrast to the overly pessimistic accounts that tend to dominate scholarly and policy debate.