States sign arms control treaties. Such treaties are advantageous for the international community as they reduce the prospect of a nuclear war. However, even if arms control treaties improves world security, it is still a puzzle why nuclear states sign and ratify such treaties when these weapons are seen as central mean of national security: Why would a nuclear state willingly limit its arsenal and constrain its own nuclear policy options? This puzzle motivates the research question of this thesis: What are the purposes of the New START Treaty for U.S. policymakers and experts? The New START Treaty expires next year and this thesis may improve our understanding of the implications of the treaty’s expiration. To answer the research question, I utilize a theoretical framework not previously applied to the case of New START. The framework directs attention to the multiple purposes for signing arms control: disarmament, strategic stability and strategic advantage. I demonstrate empirically the presence of five purposes among U.S. policymakers and experts in the Senate hearings before the New START Treaty was ratified. A first purpose, was to enhance U.S. international disarmament credentials. A second purpose was to spur continuing bilateral disarmament efforts. Third, it was hoped that the treaty´s transparency measures would increase predictability, which would maintain strategic stability. Fourth, one wanted to reduce and regulate weapons in order to maintain strategic stability at a lower cost. Fifth, policymakers and experts expressed underlying concerns with enhancing U.S. strategic advantage. If the New START Treaty expires next year, it might no longer serve the U.S. these purposes.