Although nuclear weapons are likely to spread to small and medium powers, the main problem for inter national security will be the effect of proliferation on the avoidance of nuclear war between the superpowers. It is therefore from their vantage point that this essay assesses the role of international organizations in a nuclear-armed world. A new class of disputes caused by violations of IAEA safe guards and permissible withdrawals from the NPT is destined to be placed on the Security Council agenda. These disputes, moreover, may provide the superpowers with the opportunity to cement their common interests in controlling the effects of proliferation. Further periodic Soviet-American confrontations of nuclear-crisis proportions are to be expected, albeit in a new political context complicated by proliferation. The UN can help resolve these, as it has past crises, by pro viding an organ of last resort, registering, implementing particular provisions of these agreements, and above all cap italizing on them to advance new resources for the promotion of international security. All of these roles could be better played if the UN established an International Nuclear Security Planning Group, to devise, plan for, and supervise the execution of measures which command great support— and superpower agreement. Anything more radical, un fortunately, would require a significant upsurge of insecurity which could only result from a boundary event such as the first use of nuclear weapons.