St. Mary's Church (Polish: Bazylika Mariacka, German: St. 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 (Danzig), Poland, which is 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. Between 1536 and 1572 St. Mary's Church was used for Roman Catholic and Lutheran services alike. Since then until 1945 it was the biggest Lutheran church in the world. It is 105.5 metres (346 ft) long, and the nave is 66 metres (217 ft) 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 Oliwa Cathedral.