The article examines the doctrinal contribution of Professor Hersch Lauterpacht to the development of International Treaty Law. Based on the analysis of Hersch Lauterpacht's scientific work in the field of international treaty law, his contribution to the development of concepts of codification and progressive development of international law, principles of interpretation, and the relationship between the principle of effective interpretation and intentions of the parties to treaty.
 It is emphasized that, according to Lauterpacht, the codification of international law is necessary for the international community as a whole, so it should be carried out within the UN and aimed at its general acceptance by states. Therefore, all states should be given equal opportunities to participate in and join the work on codification.
 It is pointed up that among the principles of interpretation of international treaties, the main of them, H. Lauterpacht singles out the principle of good faith. The scholar considers this norm as one of the general principles of law recognized by civilized states in the matter of interpretation.
 Particular attention is paid to the doctrinal views of H. Lauterpacht on the relationship between the principle of effective interpretation and the intentions of the parties to the agreement. The researcher has noted that the intention of the parties should be a primary factor in the interpretation of agreements. According to H. Lauterpacht, in the interpretation of treaties, any considerations - effectiveness or inefficiency - which tend to turn certain intentions of the parties into a factor of secondary importance, are incompatible with the true purpose of interpretation. In fact, applying the principle of efficiency, the court does not replace the intentions of the parties and does not replace it with a third factor. Professor H. Lauterpacht, exploring the relationship between the principle of efficiency and the common intention of the treaty parties raises one of the most controversial and elusive issues of jurisprudence - the nature and limits of the judicial function. In his view, this function is largely to interpret the rule of law, regardless of the source in which it is set out. In the international sphere, the problem is complicated by the existence of a number of factors, such as the lack of common intention of the parties directly related to the subject matter of the dispute; international treaties or individual provisions are often a political substitute rather than a legal expression of the agreement of the parties.