With the possible exception of climate change, weapons of mass destruction are probably the only thing on the planet that could conceivably mean curtains for all of us. Yet Britain has relied on its nuclear arsenal for decades, and other states seem anxious to acquire one. Why do some countries have these things? What, if anything, should we do about them? How should we feel about their spread? These are some of the questions we will examine in this module. The goal is to familiarise you with the policy issues and the theoretical debates underlying them.