Works of Protestant reformers in the collections of the Lutheran High School in Mediaș. Since 2018, our research has been conducted in the historical libraries of Transylvania, focusing on the works of fifteen Western European Protestant theologians, known as reformers, who were active in the 16th century. At the Lutheran Gymnasium library in Mediaș, we discovered 58 theological texts by these authors. This number is representative of the average size of the collections we have examined. Notably, three-quarters of the works we reviewed are attributed to just three of these authors: 19 works by Melanchthon, 16 by Calvin and 10 by Luther. The number of writings by the other authors is much smaller: 4 from Musculus, 3–3 from Aretius and Brenz, and 1–1 from Bèze, Chyträus and Zanchi. Almost three quarters of these publications, 43 in all, were brought to the Carpathian Basin before 1601, mostly in the second half of the 16th century. The collection boasts a number of intriguing finds, including Melanchthon's "Loci Communes," once owned by Bartholomäus Altenberger, the reformer of Mediaș. Additionally, it features two volumes penned by Calvin, associated with Péter Csókás Laskó, who notably co-edited the Calepinus-dictionary. The majority of the Reformed texts were incorporated into the collection during the latter parts of the 17th century, serving prior to that as essential handbooks for the local clergy.