Missile defence plays an increasing role in NATO and in most US alliances in Asia, which raises the question of what impact it has on the management of extended deterrence. Extended deterrence relies on the threat of escalation. Since the costs of escalation are different for different allies, the management of extended deterrence is inherently difficult. Missile defence shifts the relative costs of conflict, and therefore also impacts on the alliance bargains that underpin agreement on extended deterrence strategy. Although increased defensive capacity is a clear net benefit, the strategic effects of its deployment and use can still be complex if, for example, missile defence increases the chances of localizing a conflict. The article discusses the role of missile defences for the US homeland, and of the territory and population of US allies, for extended deterrence credibility and the reassurance of US allies in Asia and in NATO. It argues that there is increased scope in strengthening deterrence by enmeshing the defence of the US homeland with that of its allies, and that allies need to pay closer attention to the way the deployment and use of missile defence influence pressures for escalation. In general, missile defence thus reinforces the need for the United States and its allies in Europe and Asia to negotiate an overall alliance strategy.