Abstract: The subject of this research is establishment and development of the principles of Soviet federalism: ideocracy, class character, proletarian internationalism, party spirit, right of nations to self-determination, two-level nature, unity of legal space, dual sovereignty, inviolability of the territory of the republics, dual citizenship, etc. The goal lies in examination of the sources, peculiarities of constitutional layout, evolution of the principles of Soviet federalism, and their role in the crisis and downfall of the Soviet federalism. The author offers the   definitions of such phenomena as the Soviet federalism and the Soviet federation, which defines the novelty of this work. Classification is given to the principles of Soviet federalism in accordance with the criteria outlined by the author: 1) by the time of emergence, the principles are divided into ideological (ideocracy, class character, proletarian internationalism, party spirit, right of nations to self-determination, etc.) and state-legal (single citizenship, inviolability of the territories of the republics, unity of legal system, supremacy of federal legislation, etc.); 2) by the method of codification, the principles are divided into constitutional (ideocracy, class character, right of nations to self-determination, etc.), and stemming from the essence of constitutional norms (asymmetry, party spirit, two-level nature). It is noted that some principles of Soviet federalism fade their significance over time (class character), while others are eliminated from the constitutional and legal practice (principle of mutual control over observance of the all-union and republican legislation). It is substantiated that Soviet federalism was jeopardized mostly by the fundamental interrelated ideological principles: ideocracy, party spirit, and right of nations to self-determination. The author’s special contribution consists in introducing archival documents into the scientific discourse.