This article is an attempt to identify the essence of new positivism, described by Ludwik Ehrlich as a method of interpretation of international law. The evolution of his views on international law is examined with respect to the place of this method from the beginning of 1920s until his retirement in 1961. The article expounds on both the theoretical and methodological aspects of new positivism, according to which judicial decisions should be taken into account in addition to international treaties and customs for the determination of international law. The question of the obligatory force of international law is discussed as being related to the principle of good faith, which is at the core of Ehrlich’s views on international law. The article offers suggestions on how the method of new positivism might be used and what tasks it can fulfil today. It also makes an attempt to critically analyse Ehrlich’s method and to characterize it both in general and in the context of the theory of international law.