Sejm in Lublin, that is how to cooperate more closely with Lithuania? The beginning of the Polish–Lithuanian Commonwealth, 1569.

This sejm was convened on 1 November 1568 to take place on 23 December 1568. The pre-sejm sejmiks were held in November and December 1568. However, the sejm began its session not until 10 January 1569. Stanisław Sędziwój Czarnkowski was elected the marshal. The deliberation revolved around the problem of strengthening the union between Kingdom of Poland and Grand Duchy of Lithuania. The real union was signed on 1 July 1569. Therefore, the Commonwealth, comprised of both countries, came into being.During the sejm in Lublin it was announced that Livonia was incorporated as the condominium of the Polish Crown and Grand Duchy of Lithuania. The legal positions of Duchy of Courland and Duchy of Semigallia were also determined. The sejm finished its proceedings on 12 August 1569.

See: Ustawodawstwo zob. Volumina Constitutionum, T. 2, cz. 1, Design and layout prepared by S. Grodziski, Irena Dwornicka, W. Uruszczak, Warszawa 2005, s. 244. Ustawodawstwo zob. Volumina Constitutionum, T. 2, cz. 1, Design and layout prepared by S. Grodziski, Irena Dwornicka, W. Uruszczak, Warszawa 2005, s. 245-268. Diariusz sejmu lubelskiego [Diary of the Lublin sejm], wyd. A. T. Działyński (Źródłopisma do dziejów unii [Written sources of the union history], cz. 3, Poznań 1856). Akta unji Polski z Litwą 1385-1791 [Polish-Lithuanian union records], wyd. S. Kutrzeba and W. Semkowicz, Kraków 1932, s. 193-373. Ustawodawstwo zob.Volumina Constitutionum, T. 2, cz. 1, Design and layout prepared by S. Grodziski, Irena Dwornicka, W. Uruszczak, Warszawa 2005, s. 216-244.