The article analyses the sources of local actors’ legitimacy perceptions towards international peacebuilding operations. Local legitimacy perceptions are increasingly recognised as shaping local behaviour towards international peacebuilding, which influences the effective functioning of the operation. Legitimacy debates in peacebuilding are either absent or imported from the literature on domestic legitimacy, without respect to the specific temporal and spatial situation of international operations. The article first explores which legitimacy sources influence local legitimacy perceptions of international peacebuilding operations. It finds that two sources are relevant: output and procedure. Second, it investigates how exactly legitimacy arises from them. In doing so, it demonstrates that output and procedure are umbrella terms comprising several sub-elements which influence legitimacy in different, sometimes contradictory, ways. Finally, the article empirically explores which of the sources are important to local actors’ legitimacy perceptions using field data from the EU peacebuilding operations EULEX in Kosovo and EUPM Bosnia-Herzegovina.