When exploring the sources of International Humanitarian Law (IHL) obligations of multinational peacekeeping forces, legal scholars have thus far focused mainly on the UN (and, to a lesser extent, NATO), whilst other organizations have remained largely in the shadows. Whereas the UN Secretary-General's Bulletin on the Observance by UN Forces of International Humanitarian Law has been widely debated and extensively investigated, little or no attention has been paid to self-regulatory solutions adopted by other international and regional organizations.This Article focuses on the European Union (EU), holding that this regional organization—by virtue of its sui generis nature and of its increasing engagement in the field of crisis management—can be regarded as one of the most interesting newcomers to the realm of jus in bello. More specifically, it looks at the EU's internal legal order with a view to verifying whether and to what extent it may complement customary IHL in regulating the conduct of the EU as a military actor. The Article surveys the primary and secondary sources of EU legislation which may prima facie spell out obligations for the EU-led troops engaged in European Security and Defence Policy military operations. Finally, the Article seeks to draw some broader conclusions on the nature of the relationship between EU law and IHL, as well as on the complementarity and inherent normative value of their sources.