With its five hundred thousand volumes, Nagykönyvtár, or the library of Református Kollégium, houses the largest collection of the Reformed Church in Hungary extant to us. In addition to the size, these were the premises where, around the end of the 17th century, the most independent domestic style of book binding was developed. Some of the books or written manuscripts preserved here are considered to be unique rarities in Europe as well as all over the world. Among other items, its collection of texts includes 39 codices written on parchment in the 1300s and 1500s; 146 pieces of so-called incunabula produced in the 1500s; 114 individual works that are available only in one single copy in the entire world, and 1600 curiosities of Hungarian letters dating back to the years before 1700.
Some manuscripts created by the former students of the college who became famous afterwards, such as Ady Endre, Csokonai Vitéz Mihály, Arany János, and Kölcsey Ferenc, are also kept here, making up a noteworthy section of the overall collection. The most precious items, however, are the manuscript map sheets produced by Nicolaus Germanus between 1450 and 1470 and the first Hungarian descriptive botany manual written by Méliusz Juhász Péter, called Herbárium, dating from 1578.