This article addresses the concept of "reprisal" under contemporary international law discussing, firstly, the definition of this concept during time of peace then in armed conflicts moving to the historical evolution of reprisal since the ancient Greeks until the present and by investigating its application in international practice through the study of the Naulilaa and the Caroline disputes.

Furthermore, the article considers the conditions under which this form of self-help (reprisal) would be a legitimate act before addressing the differences between reprisal and other forms of self-help such as retaliation, self-defense, reciprocity, and war. Then, the research discusses the legal status of retaliation under international law, through exposure of the position of the fathers of international law, and that of traditional scholars of international law from this concept, and then monitor the position of the League of Nations, and the Charter of the United Nations, the international Court of Justice from him, as well as the United Nations General Assembly resolution on Principles of international Law concerning friendly Relations and Cooperation among States, and finally the Final Charter of Helsinki. In conclusion, this article finds the lack of legitimacy of the armed retaliation under Contemporary International Law