Ultimata feature as a core concept in the coercive diplomacy scholarship. Conventional wisdom holds that pursuing an ultimatum strategy is risky. This book shows that the conventional wisdom is wrong on the basis of a new dataset of 87 ultimata issued from 1920–2020. It provides a historical examination of ultimata in Western strategic, political, and legal thought since antiquity until the present, and offers a four-pronged typology that explains their various purposes and effects: 1) the dictate, 2) the conditional war declaration, 3) the bluff, and 4) the brinkmanship ultimatum. The book yields a better understanding of interstate threat behaviour at a time of surging competition. Background materials can be consulted at www.coercivediplomacy.com.