The book assesses the law on the use of force under the UN Charter in curbing terrorism in particular. The main question addressed is whether the UN Charter contains provisions to curb terrorism as well as exploring the UNSC Resolutions to that effect. It also assesses the lawfulness of the use of force against terrorism done by the US and its allies. It further focuses not only on this specific use of force, but also on the changing nature of conflict, definition of terrorism and on the historical evolution of limitations on the use of force, from 1945 until to date. In the five Chapters which traces the timeline development of international law and use of force in curbing terrorism, limitations on the resort to force in particular to combat terrorism, the use of force in self defense, pre-emptive self defense, the use of forcible measures short of war, and the use of force in response to non-state actors.