After more than three decades of on-off negotiations, a CTB treaty was signed in 1996. This book describes how the CTB will affect nuclear programmes and decision-making in the nuclear weapon states, the threshold states and the non-nuclear weapon states of proliferation concern. While some states will maintain their nuclear weapon arsenals and options under the CTB - and some weapon modernization may be undertaken - the CTB will foreclose a number of technologies and will probably be signed and ratified.Further the CTB will codify a norm against nuclear modernization and strengthen the norm against nuclear proliferation in a way that reinforces other efforts to restrict nuclear activities. The book examines the significance of treaty provisions that may be intended to accommodate existing nuclear weapon stockpiles or options and how these provisions may function as modernization or proliferation loopholes. It concludes with a review of practical steps that can be taken - both unilaterally and multilaterally - to further strengthen these norms and reinforce the CTB regime.