The article examines the problems of defining the subject of municipal law as a branch of Ukrainian law. The phenomenology of municipal law is studied in the context of its genesis, development and understanding of the subject of municipal legal regulation. It is proved that the subject of municipal law as a branch of national law should be considered social relations that arise in the process of recognition, formation, organization and exercise of municipal power, as well as the realization and protection of municipal human rights. The article provides a doctrinal analysis of approaches to interpreting the content of relevant social relations. The issue of the principles and forms of implementation of municipal law was raised.
 It is stated that the urgent task of the modern municipal legal doctrine is the search for the main characteristics of the subject of municipal legal regulation, that is, the generalized criterion that allows to attribute the social relationship to the number of proper municipal legal relations. Municipalism and community organization at the municipal level - the municipal system - should act as such a characteristic.
 For the first time, it was proposed to introduce the category «municipal system» into scientific circulation. According to the author, the municipal system is a system of social relations and principles related to the exercise by territorial communities of their functions and powers as the primary subject of local self-government, as well as the implementation of historical, socioeconomic, spiritual-cultural, ethno-national and other features and traditions of their municipal life, which are recognized and protected by the Constitution and other acts of positive law. It is a kind of system-conglomerate structure, a synergistic combination of the principles of local self-government and heterogeneous elements and processes of municipal life (human rights, freedom, democracy, power, territory, property, etc.). It is claimed that the municipal system is one of the basic criteria for the formation of the subject of modern municipal law.