This article maps the range of war crimes being committed in Syria with reference to the applicable treaty and customary international law and prospects for prosecution. It begins by presenting the international legal framework employed to determine when an armed conflict began in Syria, how this conflict is classified under international law and which multilateral treaties and customary rules are operative. This framework underlies the determination of which war crimes can be prosecuted, which tribunals might have jurisdiction and which perpetrators may be made subject to indictment. The article next focuses on some open legal and factual issues around certain war crimes that are particularly salient in the Syrian conflict but that have been under-theorized and rarely prosecuted. Along the way, it demonstrates that many of these war crimes could not be easily prosecuted before the ICC or under any domestic war crimes statutes that hew closely to the law of war treaties given the stark divergence between treaty law and customary international law when it comes to non-international armed conflicts in general and to the prosecutability of war crimes in such conflicts in particular. These observations offer support for proposals to develop an ad hoc tribunal dedicated to the Syrian conflict, as sketched out in the final section. All told, the article demonstrates the continued utility of customary international law to ensure that courts can enforce evolutions in the law notwithstanding the tendency of treaties toward normative ossification.