In this paper we have analyzed one of the major issues for international law public: the principle of pacta sunt servanda. In the international legal order a special place is occupied by the fundamental principles of public international law, as normative prescriptions with universal application, which have an imperative character and a maximum of generality and are intended to protect values, fundamental in the relations between the subjects of international law. The principle of pacta sunt servanda, alongside the other principles of international law, lies at the foundation of the entire legal building of international relations society and ensure international legality, peace, peaceful co-operation between states. We will examine, among other things, the origin of this principle, its legal consecration in international documents, its character by jus cogens, its action on relations between states, but also the limits of pacta sunt servanda.For the elaboration of the paper we have used as research methods the analysis of problems generated by the mentioned subject with reference to doctrinal views expressed in treaties and papers, the documentary research, the interpretation of legal norms in the matter.