Proliferation resistance has been debated for decades. If international proliferation resistance is to be achieved, the approach will need to involve intrinsic (technological) and extrinsic (institutional) factors. Because there are no simple technological "fixes," extensive analyses and research and development are required to determine the effects of both factors on any proposed approaches for proliferation resistance, particularly their effectiveness, cost, and operational impacts. In support of this goal, a promising evaluation methodology has been developed and is being improved by the Proliferation Resistance and Physical Protection Working Group of the Generation IV International Forum.