Deterrence is back on the international political agenda. The reappearance of geopolitical competition and great power brinkmanship has rekindled interest in the theory and practice of deterrence. Deterrence has also returned as a guiding concept in the strategic postures of major military powers. It is central to NATO's efforts to meet Russia's resurgence, it permeates Russia's military (and other) efforts to holdoff what it sees as a revisionist West, it remains a cornerstone of US grand strategy under Trump, and it is part and parcel of the doctrines of emerging great powers like China and India. A new wave of academic writings on deterrence acknowledges that deterrence has become far more difficult to achieve in the current polycentric and still highly interconnected world, in which actors draw on a much broader portfolio of instruments of statecraft in the context of cross domain strategies. Authors therefore agree that effective deterrence requires the development of new concepts to tackle the fundamentally different challenges in today's security environment.