The subject of this research is the historical-legal grounds of rendering mutual legal assistance in the Republic of Azerbaijan. Research methodology is comprised of formal-legal, comparative-legal, and historical-legal methods. Normative framework is formed by the Constitution, provisions of the criminal procedure legislation and laws, international acts acceded by the Republic of Azerbaijan, which regulate mutual legal assistance issues. Objective: to develop proposals for improving the Institute of mutual legal Assistance. assistance in criminal matters based on the historical experience in this field. The research results are as follows: mutual legal assistance has evolved from elementary extradition of fugitive serfs, one-time provision of diplomatic assistance to institutionalized legal assistance based on multilateral and bilateral agreements; from the absence of  legislative framework to codification; from inclusion of separate norms on certain aspects of the agreement on friendly relations, peace, cooperation or even submission to conclusion of special bilateral agreements. The acquired results can be implemented in intergovernmental relations regulation of rendering mutual legal assistance in criminal matters. The novelty of this research consists in consideration of legal assistance based on the historical-normative acts of the Republic of Azerbaijan. The following conclusions were made: in some historical periods, legal assistance included such institutions as the presence of state representative of the accused in administration of justice against a foreigner, unconditional extradition of criminals who committed grave crime, stiff punishment of those reluctant to peace, elimination from jurisdiction of certain criminals, transfer of prosecution, etc. can still be currently used to regulate or improve the institution of legal assistance in criminal matters, including reasonable terms for submitting court requests. For example, a reasonable term for criminal proceedings is one of the guarantees of effective legal proceedings, the violation of which also entails an infringement of such a fundamental right to fairness of proceedings.