The Treaty of Melno (; ) or Treaty of Lake Melno was a peace treaty ending the Gollub War. It was signed on September 27, 1422, between the Teutonic Knights and an alliance of the Kingdom of Poland and the Grand Duchy of Lithuania at Lake Melno (German: Melnosee, Meldensee; Polish: Jezioro Melno), east of Graudenz (Grudziadz). The treaty resolved territorial disputes between the Knights and Lithuania regarding 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 partially survives as the border between the Republic of Lithuania and Kaliningrad Oblast, Russia, making it one of the most stable national borders in Europe.