The Department of Manuscripts and Early Printed Books of the National Library of the Czech Republic started in 2017 a systematic and comprehensive research of provenance glosses in medieval manuscripts and incunabulas deposited in the historical collections of the National Library. The primary goal of the project is to complete all medieval provenance glosses and to identify the private and institutional owners. First, data from available sources (i.e. all known and available printed catalogs and descriptions in digital databases and virtual libraries) are being reviewed, supplemented or/and corrected. The newly found glosses in manuscripts have been rewritten in accordance with the XML-structure used for virtual library of historical collections Manuscriptorium (in accordance with the TEI Guidelines P5). Glosses in incunabulas will be processed in Aleph platform (MARC21). In the last year of research, all completed records will be uploaded to the virtual library Manuscriptorium, hosted in the National Library CZ. The team has been continuously working on the identification of individual owners and ownership institutions, that will be shared with CERL Thesaurus. The ideal goal is to complete the original libraries, which were scattered in historical collections of the National Library (including geolocations). The reconstructed virtual medieval libraries will be accessible in the Manuscriptorium . This comprehensive research will allow further identification of significant cultural persons, geolocations, former libraries. This key research will complement existing scattered information about many original manuscripts and incunabulas and extend next research.