Why do states start wars that they ultimately lose? Why do leaders often possess inaccurate expectations of their prospects for victory? The central argument of this book is that institutional variation in how political leaders and bureaucracies relate to one another shapes the propensity for miscalculation at the onset of international conflict. The same institutions that provide the best information also empower the bureaucracy to punish the leader. Thus, miscalculation on the road to war is often the tragic consequence of how leaders resolve the trade-off between good information and political security. This chapter provides an overview of central concepts, briefly summarizes the argument, discusses the contributions of the theory and findings to the field, and details a roadmap of the remainder of the book.