The international treaty is a means of co-operation between states and an efficient and precise method of regulating relations between them. International treaties are of paramount importance in the conduct of international relations, and as a legal source their influence is constantly growing. It is essential in the study and application of the law of international treaties to take into account that the international treaty is a manifestation of sovereignty.
Their role in public international law is manifested under two main aspects: on the one hand, it contributes to the codification of law, and on the other hand it contributes to its progressive development. While codification leads to greater accuracy of regulations, progressive development leads, in principle, to an increase in the quality of international law, both vertically and horizontally. There are currently areas that are inconceivable in the absence of international treaties (such as human rights, international law, international investment and international trade, international transport and communications, cyber security, etc.). The codification of the law of treaties was accomplished by the 1969 Vienna Convention on the Law of Treaties, without exhausting all issues arising from the conclusion, execution, amendment or termination of international treaties. Knowledge of treaty law is essential for understanding how international relations and international law work (even if we are in a sphere of social relations in which the presence of the political factor is constant), but also for understanding the interdependencies between international law and domestic law. states. The role of treaty law is not limited to its contributions in relations between states, but on the contrary it is growing. The law of treaties has the vocation to regulate absolutely all the relations that take place between entities that have international capacity (international governmental organizations, peoples fighting for liberation), even if there are divergent opinions on these aspects. Indeed, sometimes the regulations of the law of treaties are only a normative loan without binding legal force.
The role of international treaties must not, at present, be reduced to the sphere of public international law. The role of international treaties in the modern period extends to the domestic law of states, even if the actual application depends on the constitutional system of each state. On domestic law, in principle, the international treaty can be manifested under the following aspects: to generate its uniformity by reference to the legal system of the other states parties; to confer on entities that normally do not have international status, specific capacities to act in the field of international relations.
The law of international treaties, as a legal discipline and subdivision of law, consists of the rules and procedure for the creation, application and termination of international treaties, including all moments of their existence. In other words, the law of treaties is a "law" of treaties. There is a distinction between this concept and the rules contained in the treaties and the meaning of the expression treaty law should not be confused with the rules contained in international treaties; the latter make up what is known as conventional international law, designating all the international legal rules that are expressed in international treaties. On the other hand, the law of treaties, although largely covered by the Vienna Convention on the Law of Treaties, its rules express general international law.