To be inscribed on the UNESCO World Heritage List, UNESCO World Heritage properties must be of Outstanding Universal Value and meet at least one of ten selection criteria. The Abbey of St. Gallen meets criteria II and IV for its inscription.
Criterion (ii): The Abbey of Gozbert (816-837) exerted a significant influence on the development of monastic architecture following the Council of Aix-la-Chapelle, as demonstrated by the famous plan of St Gall of the 9th century, which comprises architectural drawings of 341 inscriptions on parchment that may be perceived as the ideal layout for a Benedictine abbey.
Criterion (iv): The Abbey of St. Gall may be considered a typical example of a large Benedictine monastery, centre of art and knowledge, with its rich library and scriptorium. In their diversity, the successive restructurings of the conventual space attest to an ongoing religious and cultural function.
Integrity: The property comprises the entire monastic ensemble with the archives of the Abbey, the Abbatial Library, and all the restructuring developments over more than 1200 years. It consequently retains all the necessary elements to express its Outstanding Universal Value.
Authenticity: The property reflects an architectural development spanning several centuries and bears witness to well-preserved material and original substance, with a continuous religious, cultural and public function.
You can find more information at whc.unesco.org.