Résumé : For some time now, the entire international community has been giving an increasingly greater amount of awareness on behalf of terrorism and international security in general; this has encouraged me to investigate what are the concrete measures that the U.N. Security Council can rely on, what has been its role and how it decided to act since 2001, with particular reference to specific cases of intervention, until 2018. The current international situation, in terms of security, is defined as one of greatest issues of world history: it would be, therefore, interesting to further examine the matter in order to legitimately balance the battle against terrorism and the legitimacy of the use of force in that context, and analyse specifically how the Security Council can do so. The objective of the investigations is to assess what have been the concrete actions of the United Nations, and more specifically of the U.N. Security Council, in the War on Terror. In order to so, I have examined how the role of the Security Council has evolved and developed since 2001, and in what ways did its interventions change following the terrorist attacks of September 11, 2001. Within this context, the legality of the use of force as supplied by Chapter VII of the U.N. Charter (as well as article 51) has presented many controversies. Furthermore, another interesting issue concerns whether the U.N. Security Council has overemphasized the War on Terror, within its role of safeguarding international peace and security.