As a research centre for the theological faculty, the library, of course, contains an extensive collection of modern and new works on theology and related disciplines, and evolves with the electronic innovations introduced into modern libraries. In addition, however, the library has a very valuable segment consisting of a collection of ca. 160,000 older printings from the 15th, 16th, 17th and 18th centuries. In 1994, to mark the occasion of the library's twentieth anniversary, Frans Gistelinck and Maurits Sabbe edited a catalogue of the post-incunabula present in this collection under the title «Early Sixteenth Century Printed Books 1501-1540 in the Library of the Leuven Faculty of Theology» (Documenta Libraria 15, published by the Theology Library and Peeters). The catalogue included 953 titles, mainly from the Jesuit collection and the library of the Archdiocese of mechelen, and further, among others, from the Franciscan Friars Minor in Vaalbeek (Leuven). This beautifully illustrated catalogue included various studies on the origin and content of the collection. Today, ten years later, this collection of post-incunabula has again grown from the addition of copies from libraries acquired later and from purchases. The library's thirtieth anniversary seemed to us to be a suitable occasion to publish a Supplement to the catalogue.