The Battle of Gumbinnen, initiated by forces of the German Empire on 20 August 1914, was a German offensive on the Eastern Front during the First World War. Because of the hastiness of the German attack, the Russian Army emerged victorious.

The Eastern Front or Eastern Theater of World War I was a theater of operations that encompassed at its greatest extent the entire frontier between Russia and Romania on one side and Austria-Hungary, Bulgaria, the Ottoman Empire, and Germany on the other. It ranged from the Baltic Sea in the north to the Black Sea in the south, involved most of Eastern Europe, and stretched deep into Central Europe. The term contrasts with the Western Front, which was being fought in Belgium and France.