For the first time, the matter of relations between the titular Polish nation and national minorities of the future independent state was declared in the Manifest of Temporary People Government of the Polish Republic on 7 November 1918. This legislative act was urging the Poles, who were located on the Lithuanian territory, to live “in brotherhood harmony with Lithuanian and Belarusian people” and seek their (Lithuanian) rebuilding. The Poles of Eastern Galicia and Ukraine were also urged to peacefully resolve controversial matters with the Ukrainian people. Article 109 of the Constitution of the Second Polish Republic of 17 March 1921 (the so-called the March one) clearly defined the rights of the national minorities: “Every citizen has the right to preserve his nationality, cherish his language and national specificities”. At the same time, it stated that future legislation would formulate main principles regarding the comprehensive development of national minorities. A separate article, 110, guaranteed the right of national minorities to found and manage different kinds of institutions, mainly of non-state character. It is worth mentioning that the national minorities were divided into national, religious, and language minorities. The Constitution of 1935 (the so-called the April one) became a step backward in determining the rights of national minorities. After its adoption, the articles devoted to minorities’ rights were revoked, instead, the constitutional generalizations as “neither origin nor religion, nor gender nor nationality may be a basis for the restriction of citizen rights”. Overall, in both Polish and Ukrainian historiography, the opinion that the April Constitution was based on the idea of subordinating individual interests (including the interest of the national minorities) to the interests of the State/President prevails. Other normative legal acts of interwar Poland were also devoted to the development and regulation of the national minorities’ processes. The factors to impact the institutional-legislative regulations in this field were national, religious, and political discrepancies in the multi-national Second Polish Republic.