"Recent press reports indicate that the Obama Administration might adopt a declaratory policy stating that the United States will not be the first to use nuclear weapons in conflict. These reports have reignited debate about the benefits and risks of this policy, known as a 'no first use' pledge. U.S. officials have repeatedly stated that the United States could, under certain circumstances, use nuclear weapons against a state, even if the latter has not already done so. The absence of a 'no first use' pledge dates back to the Cold War when the U.S. sought to deter a Soviet attack on the United States and its allies in Europe. The United States has modified its policy to reduce the apparent role of nuclear weapons, but has still not declared that it would not use them first."
CRS Insight, IN10553
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html