Nuclear weapons have lost none of their capacity to stir serious debate among scholars and policy-makers. Despite the passage of time since the Cold War-a period during which the harsh reality of mutual assured destruction pervaded relations between the superpowers-there remains a wide gulf dividing both policy-makers and non-government experts over what the appropriate role for nuclear weapons should be in the twenty-first century. This debate has ebbed and flowed over the past two decades and has been characterized by surges of optimism from those who believe nuclear weapons will be consigned to the dustbin of history in the near future and matching surges of pessimism from those who maintain that nuclear weapons will always be with us.In recent discussions, significant attention has focused on the issue of nuclear deterrence and the closely related question of whether security guarantees from nuclear weapon states to non-nuclear weapon states involving the possible use of nuclear weapons have a place in the twenty-first-century global strategic landscape. While some have sought to highlight what they see as the continuing utility of extended nuclear deterrence, other contributors to the literature remain sceptical that it has a role to play in stabilizing strategic relationships among states. Some, indeed, argue that extended nuclear deterrence constitutes a major obstacle to reducing the salience of nuclear weapons worldwide. According to this perspective, by reifying nuclear deterrence as a dimension of the security guarantees that lie at the heart of its alliance networks, the United States is effectively blocking progress towards bringing the number of nuclear weapons down to levels where complete disarmament can become a feasible option for policymakers. 1 Others have even claimed that, given doubts about whether any US administration would actually consider employing nuclear weapons in situations other than when American territory is threatened directly by a nuclear-armed adversary, extended deterrence is merely a rhetorical device designed to shore up alliances. As one leading expert has observed, 'there is no such thing as "the nuclear umbrella" … one US administration after the other has told allies what they wish to hear, calculating that a little loose rhetoric is surely less harmful than * This article was written as part of an Australian Research Council project (LP0883246). 1 See e.g. Ivo Daalder and Jan Lodal, 'The logic of zero: toward a world without nuclear weapons ', Foreign Affairs 87: 6, Nov.-Dec. 2008, pp. 80-95.