Abstract The Chemical Weapons Convention remains a landmark international treaty. It was the first multilateral agreement to ban an entire class of weapons of mass destruction and include a strict verification regime to monitor compliance. Scientists were not only deeply engaged in the negotiation of the Chemical Weapons Convention, but have been central to the life of the Organization for the Prohibition of Chemical Weapons (OPCW) ever since it came into existence almost 20 years ago. Over that time, during which the OPCW focused primarily on its mission to oversee the destruction of chemical weapons stockpiles, the organization has relied on a very committed core of scientific expertise – from within and outside – to help guide it. As that core task comes to a close, the Organization faces a new challenge: ensuring that chemical weapons do not return. Meeting that challenge will require new approaches to the OPCW’s mission.