The Old Synagogue (Polish: Synagoga Stara) was an Orthodox Jewish synagogue situated in the Kazimierz district of Kraków, Poland. In Yiddish it was referred to as the Alta Shul. It is the oldest synagogue building still standing in Poland, and one of the most precious landmarks of Jewish architecture in Europe. Until the beginning of the Second World War in 1939, it was one of the city's most important synagogues as well as the main religious, social, and organizational centre of the Kraków Jewish community.

The Synagogue was built in 1407 or 1492; the date of building varies with several sources. The original building was rebuilt in 1570 under the watchful eye of an Italian architect Mateo Gucci. The rebuilding included the attic wall with loopholes, windows placed far above ground level, and thick, masonry walls with heavy buttressing to withstand siege, all features borrowed from military architecture. There was further reconstruction work in 1904 and in 1913. The Old Synagogue is a rare, surviving example of a Polish fortress synagogue. In 1794 General Tadeusz Kościuszko spoke from the synagogue to gain the Jewish support in the Kościuszko Uprising. A plaque in the entrance hall commemorates this event: