Abstract In 2016, the United Kingdom and countries from the European Union announced plans to use development aid to mitigate migration from Africa. Among the countries they target are several with ongoing civil wars. I investigate this policy option—giving development aid to a country in an ongoing civil war—and its implications for migration. I theorize that when countries send development aid to countries in civil war, that development aid alters how much in resources the government, and in response a rebel group, strategically invest in fighting. Even with increased investment in fighting, it is possible that development aid can bring sufficient benefits to offset violence and decrease migration. But the critical factor in whether development aid decreases migration or not is the relative efficiency with which the government and the rebel group fight and produce. I find evidence for the theory. On average, outflows during a civil war are reduced with increased development aid. However, the reductions are small—on the order of hundreds of people per millions of dollars. Furthermore, I find evidence for the efficiency condition in the theory. I argue that governments should be cautious in pursuing a strategy of providing aid to mitigate conflict-driven migration, given the small average effects. In addition, the problems with measuring the relative production technology of rebel groups may make targeting aid at the right conflicts prohibitively difficult.