Global politics in the twenty-first century is complicated by dense interdependencies, rapid technological innovation, and fierce security competition. How should governments formulate grand strategy in this complex environment? Many strategists look to deterrence as the answer, but there are doubts about how much we can expect from deterrence. Classical deterrence theory developed in response to the distinctive circumstances of the Cold War. Since then, strategists have sought to apply deterrence theory to a range of threats on the land, sea, air, space, and cyber domains, with varying degrees of success. If war is the continuation of politics by other means, then the diversity of technologies in modern war suggests a diversity of political effects. Some military forces or postures are particularly useful for “winning” wars. Other military and non-military tools are more adept at “warning” adversaries of consequences or demonstrating resolve. Still others may accomplish these objectives at a reduced political cost, or with greater strategic stability. As such, deterrence is not a single, coherent strategy or objective, but a complex bundle of relationships between and among several ends and means. This book presents findings from a decade-long research program on “cross-domain deterrence.” Through a series of theoretical and empirical studies, it explores fundamental trade-offs that have always been implicit in practice but that have yet to be synthesized into a general theory of decision making under constraint and in the pursuit of peace. It integrates newly revised and updated versions of published work alongside new work into a holistic framework for understanding how deterrence works—or fails to work—in multiple domains.