Ossiach Abbey is a former Benedictine monastery in Carinthia. Ossiach was founded by Otto III and is considered the oldest Abbey of Carinthia.

According to the legend, the Polish king Boleslav II the Bold was expelled in the year 1079 for the murder of St. Stanislaus, and fled to Hungary, and then wandered through Europe and found peace, finally, when I arrived in Ossiach. The king lived in a monastery as dumb, repented for eight years, humbly performed the complex work, while on her deathbed she told her Confessor who he is and what he did for repentance. The inscription on his tomb, located on the North side of the Church building, says: "Boleslav, king of Poland, the murderer of St. Stanislaus, Bishop of Cracow".

Itself the Romanesque Church was first mentioned in 1215. Rebuilt in the late Gothic style after a fire in 1484.

When the Abbot Werner (1307-1314) in Ossiach began a centuries old tradition of miraculous healings. The legend says that Werner received three crystal spheres from the Mother of God to heal the blind, deaf, and dumb. To this day preserved only the smallest of the three spheres that are kept in the Diocesan Museum in Klagenfurt.

In 1484, the monastery and Church were almost completely destroyed by fire. Abbot Leonard Zorn resigned in the same year, and his successor, Daniel Berger Barney (1484-1496) began to rebuild the Abbey.

Ossiach Abbey was dissolved in 1783 during the reign of Joseph II, after which the building was used as barracks. The library was destroyed, and most of the books were transferred to the University of Graz. The Church became a parish.

In 1816 the premises was largely destroyed. Between 1872 and 1915, over the years the few remaining buildings were re-used as a barracks and a stable. Since 1995, the premises were transferred to the administration of Carinthia. It also hosts an annual music festival.