This report provides up-to-date information on the four main technical issues which will present the greatest challenges to the implementation of the comprehensive test ban treaty being negotiated at the Geneva Conference on Disarmament: formulating an appropriate definition of the term nuclear test; creating the organization for effective implementation; verifying compliance with the treaty's provisions; and implications of the treaty's prohibition on preparations for testing, whether that prohibition is made explicit or remains implicit. The report is written in such a way that it offers important background to the non-specialist while providing timely guidance to policy-makers and others involved in the public debate of these issues. It is designed to support prompt completion of the treaty by suggesting ways in which disputes over contentious issues can be resolved speedily.