The Treaty of Melno or Treaty of Lake Melno was a peace treaty ending the Gollub War. It was signed on 27 September 1422, between the Teutonic Knights and an alliance of the Kingdom of Poland and the Grand Duchy of Lithuania at Lake Melno, east of Graudenz (Grudziądz). The treaty resolved territorial disputes between the Knights and Lithuania regarding Lithuania Minor and Samogitia, which had dragged on since 1382, and determined the Prussian–Lithuanian border, which afterwards remained unchanged for about 500 years. A portion of the original border survives as a portion of the modern border between the Republic of Lithuania and Kaliningrad Oblast, Russia, making it one of the oldest and most stable borders in Europe.

The Golub War was a two-month war of the Teutonic Knights against the Kingdom of Poland and the Grand Duchy of Lithuania in 1422. It ended with the signing the Treaty of Melno, which resolved territorial disputes between the Knights and Lithuania over Samogitia that had dragged on since 1398.