The return of great power competition is reinvigorating the study of military alliances. In this article, Dr Pilster reviews three remarkable books from recent years: A. Wess Mitchell and Jakub J. Grygiel’s “The Unquiet Frontier” (2017); Mira Rapp-Hooper’s “Shields of the Republic” (2020); and Alexander Lanoszka’s “Military Alliances in the Twenty-First Century” (2022). The authors straddle academia and policy: Lanoszka is a political scientist with a specialisation in alliances; Grygiel, Mitchell, and Rapp-Hooper all served in the US State Department; and Mitchell was co-chair of the independent reflection group on NATO 2030. The common denominator among the three books is that they systematically analyse the benefits, costs, and challenges of the Western alliance system.