The Anglo-Soviet Treaty, formally the Twenty-Year Mutual Assistance Agreement Between the United Kingdom and the Union of Soviet Socialist Republics, established a military and political alliance between the Soviet Union and the British Empire.

The Anglo-Soviet Agreement was a declaration signed by the United Kingdom and the Soviet Union on 12 July 1941 to cooperate in the war against Nazi Germany. Shortly after the beginning of Operation Barbarossa, the German invasion of the Soviet Union, both powers pledged to assist each other and not to make a separate peace with Germany.