This book is about the present and future of US extended deterrence commitments in the NATO alliance. NATO is a mutual security treaty backed by the full range of US and allied military capabilities, and the hope has always been that by extending this military umbrella, especially nuclear weapons, adversaries would be deterred from attacking allied countries. Extended deterrence in NATO has been enormously successful, but today its commitments are strained by military budget cuts, anti-nuclear sentiment, and the US shift away from European security during the 2000s and more recently with the Asia pivot. The resurgence of Russia, however, has at least temporarily reinvigorated NATO and made extended deterrence commitments seem more important but also more risky. This book engages in a cross-sector intellectual exercise, bringing together experts from academia, think tanks and the policy world from the United States, Canada, and Europe to assess the future of US-NATO extended deterrence for regional and international security. The volume also tackles important and controversial debates about the role of nuclear weapons and missile defense, as backbone capabilities in support of extended deterrence.