In 2013, the Organization for the Prohibition of Chemical Weapons (OPCW) was awarded the Nobel Peace Prize for its work in eliminating many of the declared chemical weapons stockpiles worldwide. In this Policy Forum, published in advance of an OPCW Meeting set to begin 19 November, Michael Crowley and colleagues highlight some of the new challenges that face this international group during a time of rapid scientific development in which the definition of armed conflict is changing, and in which the broader international security environment is unstable. The authors offer key recommendations to ensure the continued prohibition of chemical weapons, in particular. Much of the OPCW's success in eliminating chemical weapons has been due to the Chemical Weapons Convention, or CWC, an international treaty of 193 participating nations that went into force in 1997. It comprehensively bans the development, production and use of chemical weapons worldwide. Later this month, the States Parties of the CWC are meeting to examine the long-term issues facing this longstanding treaty. Crowley et al. argue that, despite the political differences among those attending this meeting, certain scientific issues must be addressed - and agreed upon - in order to prevent the re-emergence of chemical weapons. According to the authors, the risks associated with toxic chemicals and their potential use as weapons are becoming less defined. As such, it is important for the OPCW to maintain and re-affirm the comprehensive nature of chemical weapons prohibition. However, some ambiguity remains in this space, as relates to toxic "non-lethal" or "incapacitating" chemicals presently used in law enforcement situations, in Russia for example. Currently, the CWC permits the use of some of these compounds, known as ICAs, which can be lethal at high doses. It is envisaged that an Open-Ended Working Group the November conference would establish would come to a determination about whether the development and use of ICA weapons for law enforcement is prohibited under the CWC, or whether such actions are permitted but should be severely restricted. Additionally, new types of chemical production processes, like bio-manufacturing, need to be evaluated and included in national verification strategies, the authors say.