Preventing nuclear war is one of the truly existential challenges facing the human species -- but the danger is rising, as tensions among nuclear powers increase, nuclear agreements are challenged, and new technologies and arms competitions create new uncertainties. From Iran to North Korea, from U.S.-Russian and U.S.-Chinese nuclear competition to Syria's deadly chemical assaults, decisions about nuclear, chemical, and biological weapons can make the difference between war or peace and between safety or grave danger for people around the world. This course will give students an understanding of these weapons and the global efforts to prevent their use and control their spread. The course covers policy tools from treaties and diplomacy to sanctions and war. This year, particular attention will be paid to emerging great-power competition and its implications for deterrence and arms control. Students will learn to use an integrated, risk-informed approach to assessing policy options when difficult choices need to be made in the face of large uncertainties. This will help prepare students for careers dealing with choices about these deadly weapons.