A Dissertation submitted in Partial Fulfillment of the Requirements for Award of the Degree of Master of Laws (LL.M) of Mzumbe University.The dissertation 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 as practices 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. Also the study discusses the UNC from its inception, including its relevant provisions which do not provide a conclusive answer, or contain any provision that deal specifically with prohibition of terrorism. The trend shows that in the course of the last two decades, the Charter regime has been re-adjusted so as to permit forcible responses to terrorism under more lenient conditions. The Charter permits two kinds of forcible measures that are; collective responses and self-defense. Hence there is significant doubt as to lawfulness of using force by states against terrorism by other means save for SC authorization. Furthermore, the study major findings and recommendation challenges the common assumption that the use of force against terrorism was an example of states exercising their inherent right to self defense, it argues that if this particular use of force is not challenged, it will lead to expansion of right of self-defense which will hinder rather than enhance international peace and security. Finally, this study draws on recent examples to illustrate the use of force against terrorism could become a dangerous precedent for the use of force especially by US and its allies. Therefore, the study recommends that the international community should condemn and ultimately abolish such an approach.