The essays in address the contribution that political theories of modern political philosophers have made to our understandings of peace. The discipline of peace research has reached a critical impasse, where the ideas of both “realist peace” and “democratic peace” are challenged by contemporary world events. Can we stand by while dictators violate the human rights of citizens? Can we impose a democratic peace through the projection of war? By looking back at the great works of political philosophy, this collection hopes to revive peace as an active question for political philosophy while making an original contribution to contemporary peace research and international relations.