The nexus between international law and municipal law is analysed in this paper. Though international law focuses on inter-State relations and municipal law on ties between citizens or between citizens and the State, several topics require international and domestic legislation, like the environment, commerce, and civil rights. Even though the international legal order maintains its priority over municipal legislation, it leaves the question of how existing international principles must be implemented or enforced in municipal charges to domestic constitutions. The link between domestic and international lawful regimes is based on two opposing doctrines: Dualism and Monism. The autonomous and separate nature of municipal legal institutions, in which the State is sovereign and supreme, is commonly referred to as Dualism. Meanwhile, monism theories see the connection between international and municipal legal orders as more united and coherent, with its legitimacy derived from a single source.