The collection includes works and translations of Protestant authors from today's Slovenian territory and some other works to which those authors contributed. In addition to the key works of the Slovenian Reformation, thus the first books in the Slovenian language, the collection also includes the Croatian Protestant prints, to which Trubar contributed. They are printed in Glagolitic alphabet, a script invented by Cyril. For many centuries it enabled to use the vernacular of the Slavs in Catholic worship. The books were published in the second half of the 16th century, some on the Slovenian territory (by Janž Mandelc printing house), others in today's Germany, in Wittenberg, and especially in Tübingen, where the works of the South Slavic Protestant authors were printed and distributed by Ulrich Morhart printing house, or by his successor Georg Gruppenbach. Digitized copies are from the Rare Prints Collection of the National and University Library, and the Royal Library of Denmark. The collection is supplemented by material digitized within the National Project for Digitization of the Slovenika (works in the Slovenian language and works on the Slovenian language and literature), and Culturally Important Library Material (2021-2030).