There is no uniform practice regarding how international treaties may become part of a municipal legal system. The principle of dualism requires a state to positively adopt a treaty as part of its law if the treaty is to have legal effect. Monism is founded on the understanding that no legislative action is needed for the reception of an international treaty into a domestic legal system. The declaration that a state is bound by a treaty makes such treaty part of its local law, and a treaty ranks above all other sources of law except the constitution of the state. Macao generally adheres to monism and there are areas where treaties are received into the Macao legal system through legislation or administrative regulation, so that courts can apply such treaty provisions in dispute settlement. This article compares the practice of treaty application in Portugal, China, Macao and Hong Kong and concludes that modification of the monist theory in Macao has much to commend.