What makes a war just? What makes a specific weapon, strategy, or decision in war just? The tradition of Just War Theory has provided answers to these questions since at least 400 AD, yet each shift in the weapons and strategies of war poses significant challenges to Just War Theory. This book assembles renowned scholars from around the world to reflect on the most pressing problems and questions in Just War Theory, and engages with all three stages of war: jus ad bellum, jus in bello, and jus post bellum. Providing detailed historical context as well as addressing modern controversies and topics including drones, Islamic jihad, and humanitarian intervention, the volume will be highly important for students and scholars of the philosophy of war as well as for others interested in contemporary global military and ethical issues.