Why did the international community respond differently to sarin use in the Syrian Civil War than to every prior case of violation of the norm against chemical weapons? Looking at the mode of response and how it differed from the international reaction to other norm violations within the same conflict suggest that the “The Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction,” often abbreviated as the Chemical Weapons Convention (CWC), served as the key factor prompting norm enforcement in this case. I argue, based upon how the CWC functioned to bring about norm enforcement in the Syrian case, that the CWC has proved more effective than past treaties banning chemical weapons for three main reasons: the backing of an actor possessing the relative power to credibly threaten enforcement of the norm, the choice of that actor to constrain itself, and the establishment of specific procedures for the norm’s enforcement including a verification regime and disarmament guidelines. The CWC’s scope, in banning chemical weapon possession in addition to use, arguably also aids the CWC’s ability to enforce the norm against use.