From the Sahel-Sahara region to Afghanistan, from Syria to the Philippines, the Internationalcommunity has been witnessing, for a number of years now, the establishment of military trainingand support partnerships, the launch of joint military operations and the formation of Internationalcoalitions which have had a recent upsurge, all of these regional having been specifically designed to fightagainst and eliminate the terrorist scourge. These different forms of military cooperation have beenjustified either by a consent or request from the territorial State, by the right of self-defense,or even by an authorization from the UN Security Council. This article's purpose is to analyzethe legal framework within which the operations must fall in order for them to be lawful andtheir justifications to be valid. Through the analysis of doctrinal debates, actual State practice andthe decisions of the International Court of Justice, this paper examines notably the criteria that makean intervention by invitation valid, the limitative conditions of invocation and implementation of theright of self-defense, and finally the original as well as the current mechanism of collective securitythat has led to the establishment of peace or multilateral operations.