Abstract: Does UN peacekeeping promote democracy in countries torn by civil war? Existing studies are limited and reach contradictory conclusions. We theorize that peacekeepers help overcome three key obstacles to democratization in conflict-affected countries: a lack of credible commitment to the democratic process, security, and capacity. We test our theory by combining three original datasets on UN mandates, personnel, and activities covering all UN missions in Africa since the end of the Cold War. Using fixed effects and instrumental variables estimators, we show that missions with democracy promotion mandates are strongly positively correlated with the quality of democracy in host countries, but the magnitude of the relationship is (1) larger for civilian rather than uniformed personnel; (2) stronger when peacekeepers engage rather than bypass host governments when implementing reforms; (3) driven in particular by UN election administration and oversight; and (4) more robust during periods of peace than during civil war.