Taking the horrific events that took place at Ypres in 1915 as its point of departure, this volume traces the development of chemical weapons from their first use as weapons of mass destruction by German troops in Belgium to their deployment in Syria in the summer of 2013. The book has emerged from a conference commemorating the centenary of the events at Ypres, held at the Fritz Haber Institute of the Max Planck Society in Berlin. The contributions focus on the preconditions and immediate consequences of this war crime, but also cover, by way of examples, the subsequent history of chemical weapons, including their role in World War II, their global spread, and their recent deployment. The volume ends with a documentation of the commemoration ceremony closing the conference, comprising speeches of the Green Cross director Paul Walker, the Belgian ambassador Ghislain D’hoop, and the Nobel laureate Gerhard Ertl.