In the wake of Russian aggression against Ukraine and the election of Donald Trump in the US, NATO faced a complex challenge: how would it defend NATO-member states bordering Russia and Ukraine, and how would it address Trump's ambiguous statements on the alliance. In this context, Deni (research professor, U.S. Army War College) makes a timely contribution to the political and analytical discourse revolving around the issues NATO faces. The book reviews NATO's evolution from an emphasis on collective defense during the Cold War, as defined in Article 5, to an emphasis on crisis management and cooperative security—including Kosovo and Afghanistan. The latter attempted to cultivate an inclusionary approach to Russia. After the Ukraine crises began, NATO returned to a focus on collective defense and addressed, again, the problems of deterring Russia. Deni's analysis not only of "NATO's Russian Problem" but also of member-state defense spending, burden sharing, and, most important, readiness to respond to challenges posed by Russia is insightful. His study concludes with a recommendation on NATO strategy emphasizing readiness. The book is well annotated and includes an extensive bibliography. It is recommended for students, researchers, and policy makers. Summing Up: Recommended. Upper-division undergraduates through professionals.