This was a roundtable convened by the Program on Humanitarian Policy and Conflict Research (HPCR) and hosted by the Geneva Centre for Security Policy. There were 4 sessions: Session 1 set the stage for the discussion, taking stock of three strands – changing war, changing actors, and stagnating law – whose challenges the meeting sought to tackle. The introductory presentation on paradigm shifts named the challenge of bridging the increasing disconnect between the way war is conceived and conducted and the manner it is regulated and codified. Session 2 reviewed the recent metamorphosis of war, identified the features and determinants of this evolution and outlined their lasting implications. Session 3 examined the problematic challenges that new forms of warfare, in particular transnational terrorism, posed to the existing body of international law. Session 4 delved into the possible legal ‘black holes’ of the law of war and the merits and demerits of an international humanitarian law regime change.