This study is designed to analyse the constitutional institution of national defence and related legal regulation and to reveal problems of legal regulation. The problems of legal regulation of national defence analysed in the research are linked by a fundamental question: what is the content of the rules forming the constitutional institution of national defence, which define the subjects of national defence and measures of national defence assigned to them by the Constitution, that determines the ordinary legal regulation of national defence? With regard to the aforementioned fundamental problem issue, the paper will aim, in particular, to analyse the concept of national defence in the broad and narrow sense, also examines the constitutional basis for the use of the armed forces as the military means of national defence. It is also analysed what state authorities take decisions on issues of national defence, first of all, on armed defence of the State, imposition of martial law or announcement of mobilisation, and how they share this authority among themselves. Also, how the democratic principle of civilian control over servicemen and paramilitary state institutions determines the distribution of responsibility for national defence between civilian and military national defence institutions. It is analysed the constitutional grounds for the universal obligation to do military service and the problems of constitutionality of some provisions of the Law on National Conscription in connection with exemption from the obligation to do military service and postponement of military service and suggests ways to solve them. Finally, it is analysed the constitutional content of the right to resist as one of the national defence measures.