The German–Soviet Boundary and Friendship Treaty was a second supplementary protocol of the Molotov–Ribbentrop Pact of 23 August 1939. It was a secret clause as amended on 28 September 1939 by Nazi Germany and the Soviet Union after their joint invasion and occupation of sovereign Poland. It was signed by Joachim von Ribbentrop and Vyacheslav Molotov, the foreign ministers of Germany and the Soviet Union respectively, in the presence of Joseph Stalin. Only a small portion of the protocol, which superseded the first treaty, was publicly announced, while the spheres of influence of Nazi Germany and the Soviet Union remained secret. The third secret protocol of the Pact was signed on 10 January 1941 by Friedrich Werner von Schulenburg and Molotov, wherein Germany renounced its claims to portions of Lithuania, only a few months before their anti-Soviet Operation Barbarossa.

The Molotov–Ribbentrop Pact, officially the Treaty of Non-Aggression between Germany and the Union of Soviet Socialist Republics, was a non-aggression pact between Nazi Germany and the Soviet Union with a secret protocol that partitioned Central and Eastern Europe between them. The pact was signed in Moscow on 23 August 1939 by German Foreign Minister Joachim von Ribbentrop and Soviet Foreign Minister Vyacheslav Molotov. Unofficially, it has also been referred to as the Hitler–Stalin Pact and the Nazi–Soviet Pact.