United Nations Security Council Resolution 1540 (2004) calls on states to prevent criminals, militant groups and other non-state actors from acquiring or using weapons of mass destruction. This monograph is based on papers that were presented and discussed at a meeting of former members of the 1540 Committee's group of experts. The meeting took place in Cape Town, South Africa in May 2015, and was organised by the ISS in cooperation with the United Nations Office for Disarmament Affairs and using funds from voluntary contributions by the governments of the Republic of Korea and the United States of America. The monograph is a timely assessment towards the 2016 Comprehensive Review of the implementation of Resolution 1540. It covers a broad spectrum of topics and recommends better ways to combat the threat of nuclear, chemical and biological weapons. The reader is invited to explore and think critically about the international community's efforts in this regard.