In the 21st century - as in the first half of the 20th century - Lithuania has faced threats posed to its national security and statehood. Owing to its limited resources, the country is not essentially able to establish large regular forces; therefore, it is permanently developing its territorial defence forces. In the interwar period, their nucleus was formed by the Lithuanian Riflemen’s Union, while in the 21st century it is by the National Defence Volunteer Forces. While modelling new concepts of territorial defence, it is inevitable to consider not only the practices of other countries and their military theories but also Lithuania’s national experience. Of course, this is the experience of 1990-2004, but in the first part of the 20th century the idea of territorial defence was also put into practice and cultivated at the theoretical level. Another aspect is that territorial defence in practice is inextricably entwined with the tactics of guerrilla warfare and their application. Lithuania’s historical experience and analysis of its territorial defence and partisan war is not only knowledge for its own sake. It may have tangible practical value since Lithuania considered, premeditated and applied these notions in practice repeatedly in the first half of the 20th century. Furthermore, the geographical location of the country and distribution of eventual sources of conflict in comparison with the interwar period have virtually not changed. In the interwar period, East Prussia, part of Germany and separated by the Polish Corridor, had been a semi-exclave up until September 1939. Similarly, it is only by sea and air that this territory is accessible at present, though now a subject of the Russian Federation as the Kaliningrad region. Due to geopolitical transformations, after World War II the ‘enemy from the East’ had moved geographically to Western Lithuania. There exists a similar situation on the south-eastern border of Lithuania, where a none-too-friendly interwar Poland changed to a Belarus governed by Alexander Lukashenko. Lithuania’s northern border with Latvia, also a NATO member at present, remains unchanged and comparatively safe; in the interwar period, only attempts were made to discuss the idea of having mutual defence although Latvia had planned to provide some support for the Lithuanian forces in the case of a Wehrmacht attack from East Prussia to the East. So it is expedient to elaborate on what attention the Lithuanian Armed Forces in the interwar period paid to the history of war, what kind of experience of the 20th century territorial defence and partisan resistance they gained, and how this may be of value to defence experts in the 21st century.