Alexander Lanoszka’s Atomic Assurance is about the alliance politics of nuclear proliferation. It centers on an elementary security relationship—between the quality of protection a country gets from others and its impulse to secure itself by arming. In this instance, the ‘protection’ is a guarantor’s policy of extended nuclear deterrence; the self-arming alternative is a nuclear weapon (or steps to obtain one). The contemporary policy relevance of Atomic Assurance is hard to exaggerate. It helps us to understand the extent to which superpower alliance guarantees did (or did not) curb allies’ proliferation during the Cold War, and whether they may do so (or not) in years ahead.