The second volume of the collection "State Borders of Belarus," which includes documents and materials reflecting the formation, change and strengthening of state and administrative borders of the BSSR and the Republic of Belarus in 1926-2010. They distinguish three blocks concerning: a) the final formation of the administrative border of Belarus with the RSFSR due to the second stage of enlargement of the BSSR (doc. No. 1-44) in 1926; b) the establishment of the western border after September 17, 1939 and the associated clarifications of the administrative and state borders with Ukraine, Lithuania and Poland in the subsequent period (doc. №45—67); c) the background of the creation, arrangement and functioning of the state border of the Republic of Belarus (doc. №68-110).