Technology has been long understood to play a central role in limiting the proliferation of nuclear weapons. Evolving nuclear technology, increased access to information, and systematic improvements in design and manufacturing tools, however, should in time ease the proliferation challenge. Eventually, even developing countries could possess a sufªcient technical ability. There is evidence that this transition has already occurred. The basic uranium-enrichment gas centrifuge, developed in the 1960s, has technical characteristics that are within reach of nearly all states, without foreign assistance or access to exportcontrollable materials. The history of centrifuge development in twenty countries supports this perspective, as do previously secret studies carried out by the governments of the United States and the United Kingdom. Complicating matters, centrifuges also have properties that make the detection of a clandestine program enormously difficult. If conditions for the clandestine and indigenous production of weapons have emerged, then nonproliferation institutions focused on technology will be inadequate. Although it would represent a near-foundational shift in nuclear security policy, the changed technology landscape may now necessitate a return to institutions focused instead on motivations.