The issue of who has the power to declare war or authorise military action in a democracy has become a major legal and political issue, internationally, and is set to become even more pertinent in the immediate future, particularly in the wake of military action in Syria, ongoing wars in the Middle East, and tense discussions between the US, its allies, Russia, and China. This book comparatively examines the executive and prerogative powers to declare war or launch military action, focusing primarily on the US, UK, and Australia.