The US has maintained nuclear forces in Europe in support of its security commitments to NATO since the early 1950s, although the number of weapons has been greatly reduced since the late 1980s. This paper examines why the Allies continue to regard US nuclear forces and commitments as essential elements of NATO's security posture, even in the profoundly changed post-Cold War international context. The main explanations for the continued relevance of US nuclear arms include: persistent uncertainties over Russia's future; potential threats in Europe's vicinity (including the proliferation of weapons of mass destruction); the continued dependence of Germany and other non-nuclear Allies on US nuclear protection; and the dangers of fundamental destabilization should the US withdraw. These factors argue that it remains in US and Western interests for the US to maintain its nuclear-weapon presence on the territory of its NATO European Allies, and to engage these Allies in nuclear-consultation and planning activities.