The Stiftskirche St. Gallus und Otmar (Collegiate Church of St. Gall and Otmar) is a Roman Catholic church in the city of St. Gallen, Switzerland.^[1] Once part of the Abbey of St. Gall, it has been the cathedral of the Diocese of St. Gallen since 1847.^[2] It is considered one of the last great sacred structures of the Baroque era, and is a UNESCO World Heritage site.

The Cathedral stands on the spot where the itinerant Irish monk Gall built his hermitage in 612. Upon his death around 650, he was buried in the oratory within his cell. Today, his tomb is located beneath the high altar in the crypt, erected 837–39.^[3]

For several decades after his death, Gall's disciples remained together at the cell he had built and followed the rule of St. Columban, combining prayer with work of the hands and reading with teaching.^[4] In 719, St. Otmar, the brotherhood's first abbot, enlarged Gall's cell into the Abbey of St. Gall.^[5] His remains are housed at the west end of the cathedral in the St.Otmar crypt, where former bishops of St.Gallen are also laid to rest.^[3]

The first abbey church was built over Saint Gall's grave around 719, and underwent a number of subsequent modifications.^[3]

Construction of the present church was initiated in 1755 by Prince-abbot Cölestin Gugger von Staudach.^[6] Completed in 1767, the cathedral was designed by Peter Thumb,^[7] who also designed the Abbey's famous library. Among its rich decorations are frescoes painted mostly by Josef Wannenmacher, and the most complete set of historic church bells in Switzerland. The south altar features a bell brought back by Saint Gall himself from Ireland, one of the three oldest surviving bells in Europe.

In 1805 the Canton of St.Gallen dissolved the abbey. After the dissolution of the monastery, the abbey church became a parish church, and with the establishment of the Diocese of St.Gallen in 1847, the cathedral.^[8]

The interior was renovated and restored to its original state between 1962–67.^[8]