Drawing upon the considerable existing body of technical material related to the Comprehensive Test Ban Treaty, the National Academy of Sciences reviewed and assessed the key technical issues that arose during the Senate debate over treaty ratification. In particular, these include: (1) the capacity of the United States to maintain confidence in the safety and reliability of its nuclear stockpile in the absence of nuclear testing; (2) the nuclear-test detection capabilities of the international monitoring system (with and without augmentation by national systems and instrumentation in use for scientific purposes, and taking into account the possibilities for decoupling nuclear explosions from surrounding geologic media); and (3) the additions to their nuclear-weapons capabilities that other countries could achieve through nuclear testing at yield levels that might escape detection, and the effect of such additions on the security of the United States.