St. Mary's Church (Polish: Bazylika Mariacka, German: Marienkirche) or, properly, Basilica of the Assumption of the Blessed Virgin Mary (Polish: Bazylika Mariacka Wniebowzięcia Najświętszej Maryi Panny w Gdańsku) is a Roman Catholic church in Gdańsk, Poland, which is claimed to be the largest brick church in the world. It was begun in 1379. (The tallest brick church is St. Martin's Church, Landshut, Germany.)
St. Mary's is one of the largest European Brick Gothic buildings, which include castles. From the Protestant Reformation in 1577 until 1945, when it was transferred back to the Catholic diocese, it was the biggest Evangelical Lutheran church in the world. It is 105.5 m long, and the nave is 66 m wide. Inside the church is room for 25,000 people. It is an aisled hall church with a transept. It is a co-cathedral in the Roman Catholic Archdiocese of Gdańsk, along with the main cathedral for the Archdiocese, the Bazylika archikatedralna w Gdańsku-Oliwie (Basilica-Cathedral of Gdańsk-Oliwa).