The subject of this study is the records of tropes to the Ordinary of the Mass in six manuscripts from the medieval Abbey of St. Gall: a total of 101 troped Kyrie, Gloria, Sanctus, and Agnus Dei, recorded by around 50 scribes. The oldest collection dates from the second quarter of the 10th century and is nearly identical in the two codices SG 484 and SG 381. Partially based on the old material, new tropes were created in the 11th century in the manuscripts SG 376, SG 378, and SG 380. This later material was expanded in the 13th century through two supplementary cycles in SG 378 and SG 382, as well as through sporadic recordings up to the 14th century. Through a codicological and paleographical examination of the St. Gall holdings and in comparison with the concordances from 220 other manuscripts, the temporal layering, provenance, dating, and function of the records are discussed. One chapter is dedicated to the topic of chant traditions and reception, and finally, the question of St. Gall's 'original creations' is explored through singular versions and unique items.