This is the first comprehensive discussion of all the main philosophical issues raised by terrorism, both conceptual and moral, against the background of its past and recent developments. Prominent philosophers and political theorists discuss definitions of terrorism, various approaches to its moral evaluation, and the contentious subject of state terrorism. Terrorism is assessed in terms of its consequences, justice and rights, and from the standpoint of just war theory. Also included are four case studies, showing how the concepts and arguments philosophers deploy in discussing violence, war, and terrorism apply to particular instances of both insurgent and state the terror bombing campaigns of World War II, Northern Ireland, the Israeli-Arab conflict, and 11 September 2001 and its aftermath.