The Diocese of Włocławek (Latin: Dioecesis Vladislaviensis) is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Poland. It is a suffragan in the ecclesiastical province of the Metropolitan Archdiocese of Gniezno. Until the 20th century, it was known as the Diocese of Kujawy.
The bishops' seat is Włocławek Cathedral, also a minor basilica: Bazylika Katedralna Wniebowzięcia NMP in the city of Włocławek, in Kujawsko-Pomorskie.
The diocese has two more Minor Basilicas:
Włocławek (Polish: [vwɔˈt͡swavɛk] ; German: Leslau or Alt Lesle, Yiddish: וולאָצלאַוועק, romanized: Vlatzlavek, Russian: Влоцлавек Vlotslavek) is a city in the Kuyavian–Pomeranian Voivodeship in central Poland along the Vistula River, bordered by the Gostynin-Włocławek Landscape Park. As of December 2021, the population of the city is 106,928.
Founded in the 9th century, Włocławek is located in the historical region of Kuyavia, and was its administrative center and main city in the Middle Ages. Nowadays, Włocławek is the third largest city of the Kuyavian-Pomeranian Voivodeship (after Bydgoszcz and Toruń) and the main cultural and economic center of eastern Kuyavia. It is the seat of the Roman Catholic Diocese of Włocławek, one of the oldest dioceses in Poland, since the 12th century, with the landmark Gothic Włocławek Cathedral listed as a Historic Monument of Poland. Poland's largest hydroelectric power plant is also located there.
The Archdiocese of Gniezno (Latin: Archidioecesis Gnesnensis, Polish: Archidiecezja Gnieźnieńska) is the oldest Latin Catholic archdiocese in Poland, located in the city of Gniezno. The ecclesiastical province comprises the suffragan dioceses of Bydgoszcz and Włocławek.