The St. Stephen's Cathedral in Passau represents the bishop's church of the largest diocese in terms of area within the Holy Roman Empire, and it is an outstanding work of Northern Alpine Baroque with epoch-making innovations in art history. On one hand, the building, thanks to its architectural plasticity and numerous stucco figures, marks the peak of stucco Baroque; on the other hand, due to its generous and innovative vault surfaces, it stands at the beginning of fresco Baroque, where ceiling painting becomes a defining factor of the space. The Baroque cathedral is fundamentally a Gothic structure that received a modern appearance after the city fire of 1662. The medieval bishop's church from the 14th to 16th centuries is also thoroughly examined in this monograph, as is the largest cathedral organ in the world and the high altar, a major work of Ars Sacra after World War II.