Church of St. Casimir, Vilnius in the context of "Vilnius"

According to the Lithuanian census of 2021, the predominant religion in Lithuania is Christianity, with the largest confession being that of the Catholic Church (about 74% of the population). There are smaller groups of Orthodox Christians, Evangelical Lutherans, members of Reformed churches, other Protestants, Jews and Muslims as well as people of other religions.

Casimir Jagiellon (/ˈkæzɪmɪər/; Latin: Casimirus; Lithuanian: Kazimieras; Polish: Kazimierz; 3 October 1458 – 4 March 1484) was a prince of the Kingdom of Poland and of the Grand Duchy of Lithuania. The second son of King Casimir IV Jagiellon, he was tutored by Johannes Longinus, a Polish chronicler, diplomat, and priest. After his elder brother Vladislaus was elected as King of Bohemia in 1471, Casimir became the heir apparent. At the age of 13, Casimir participated in the failed military campaign to install him as King of Hungary. He became known for his piety, devotion to God, and generosity towards the sick and poor. He became ill (most likely with tuberculosis) and died at the age of 25. He was buried in Vilnius Cathedral. His canonization was initiated by his brother King Sigismund I the Old in 1514 and the tradition holds that he was canonized in 1521. Saint Casimir the Prince is the patron saint of Poland, Lithuania and Lithuanian youth and the only saint with this name.

Veneration of Casimir saw a resurgence in the 17th century when his feast day was confirmed by the pope in 1602 and the dedicated Chapel of Saint Casimir was completed in 1636. Casimir became a patron saint of Lithuania and Lithuanian youth. In Vilnius, his feast day is marked annually with Kaziuko mugė (a trade fair) held on the Sunday nearest to 4 March, the anniversary of his death. There are more than 50 churches named after Casimir in Lithuania and Poland, including Church of St. Casimir, Vilnius and St. Kazimierz Church, Warsaw, and more than 50 churches in Lithuanian and Polish diaspora communities in America. Women's congregation Sisters of Saint Casimir was established in 1908 and remains active in the United States.

The Vilnian Baroque (Lithuanian: Vilnietiškas barokas, Polish: barok wileński) or the School of Vilnius Baroque (Lithuanian: Vilniaus baroko mokykla, Polish: wileńska szkoła baroku) is a name of late Baroque architecture style in Catholic church architecture of the Grand Duchy of Lithuania, which expanded well into Greek Catholic church architecture on territories covered by the Union of Brest. The style was formed by alumnus of the Catholic Jesuits' Vilnius University. Most preserved buildings in this style are in Vilnius.

The architect Johann Christoph Glaubitz is considered one of the founders of Vilnian Baroque. Working on the restoration of churches in Vilnius, he was often inspired by contemporary buildings of Austria and Bavaria. Polish churches created by Paolo Fontana [it] are also made in Vilnian Baroque style. Although being predominantly Catholic style of architecture, Vilnian Baroque was also popular among the Uniates, which gave the style its second name ‘Uniate Baroque’. Another famous architect Thomas Zebrowski also designed and supervised constructions of Vilnian Baroque churches in Lithuania and Belarus.