The Comprehensive Nuclear Test Ban Treaty (CTBT) was ratified by the United Nations in April 1996 158-3. It requires that 44 nuclear capable countries ratify it in order to go into effect. Once in effect, a global effort will be taken to monitor and stop all nuclear testing across the globe. If it is ratified, it will undoubtedly be a huge step in the right direction for humanity.
Currently, 75 countries, 43 nuclear capable countries have ratified the treaty. The hesitant country? Why, the good old USA of course. After rigorously supporting the treaty all through its tenure up until its passing vote by the General Assembly. However, the United States Congress failed to ratify the CTBT in summer of 1999. Without the support of the world's lone superpower, this treaty is all but dead. Alas, what a pity.