Jaan Poska VR III/1 (24 January [O.S. 12 January] 1866, Laiusevälja, Kreis Dorpat, Governorate of Livonia – 7 March 1920, Tallinn, Estonia) was an Estonian barrister and politician.

In 1890, Poska graduated from the faculty of Law of the University of Tartu, after that he worked as barrister in Tallinn. Jaan Poska was mayor of Tallinn during 1913–1917. In that position he supported reforms, like reforming healthcare and founding two schools. In April 1917, he became governor of the Autonomous Governorate of Estonia. 28 November [O.S. 15 November] 1917 the Maapäev refused to recognize the new Bolshevik rule and proclaimed itself the supreme legal authority of Estonia. The Republic of Estonia formally declared independence on 24 February 1918, only to be occupied by the German Empire until the end of World War I.

On 24 February 1918, Poska was appointed the Minister of Foreign Affairs of Estonia. He worked in Western Europe for gaining diplomatic recognition to Estonia and participated in Paris Peace Conference. He led the peace talks with Soviet Russia and achieved Treaty of Tartu which was signed on 2 February 1920.