The shifting security environment has revealed emerging challenges to and increased pressure points on the system of restraint, which shapes nations’ behavior and encourages restraint through several different, often mutually reinforcing mechanisms: taboos, lack of benefit, norms, and deterrence. This study examines the evolving and changing nature of chemical weapons and how the system of restraint must adapt to ensure that the proliferation and use of chemical weapons do not reemerge as endemic features of the global security landscape. The study provides a framework for structuring the problem, identifies gaps and challenges, and puts forward options for improving the global effort to prevent the proliferation and use of these weapons. Download the full report.