The Lithuanian–Soviet War or Lithuanian–Bolshevik War was fought between newly independent Lithuania and the Russian Socialist Federative Soviet Republic in the aftermath of World War I. It was part of the larger Soviet westward offensive of 1918–1919. The offensive followed the retreat of German troops and sought to establish Soviet republics in Ukraine, Belarus, Lithuania, Latvia, Estonia, Poland and link up with the German Revolution. By the end of December 1918 Soviet forces reached Lithuanian borders. Largely unopposed, they occupied one town after another and by the end of January 1919 controlled about two thirds of the Lithuanian territory. In February, the Soviet advance was stopped by Lithuanian and German volunteers, who prevented the Soviets from capturing Kaunas, the temporary capital of Lithuania. From April 1919, the Lithuanian war went parallel with the Polish–Soviet War. Poland had territorial claims over Lithuania, especially the Vilnius Region; these tensions spilt over into the Polish–Lithuanian War.

The Soviet westward offensive of 1918–1919 was part of the campaign by Soviet Russia into areas abandoned by the Ober Ost garrisons that were being withdrawn to Germany following that country's defeat in World War I. The initially successful offensive against the Republic of Estonia ignited the Estonian War of Independence which ended with the Soviet recognition of Estonia. Similarly, the campaigns against the Republic of Latvia and Republic of Lithuania ultimately failed, resulting in the Latvian–Soviet Peace Treaty and Soviet–Lithuanian Peace Treaty respectively. In Belarus, the Belarusian People's Republic was conquered and the Socialist Soviet Republic of Byelorussia proclaimed.