The Lobkowicz Library (i.e. the library of the Roundice branch of the House of Lobkowicz), with approximately 65,000 volumes—including 730 incunabula and 679 manuscripts—is the largest aristocratic castle library in Czechia and one of the oldest in Central Europe. Its origins date back to the 14th century, with its intellectual foundation laid by the humanist poet and philosopher Bohuslav Hasištejnský of Lobkowicz, who amassed the largest humanist library of his time. Systematic expansion began in the 17th century under Zdeněk Vojtěch and Polyxena of Lobkowicz, incorporating entire libraries through inheritance and acquisition, especially following the 1620 defeat of the Bohemian estates. The collection moved to Roudnice Castle in 1657 under Václav Eusebius, who introduced the first comprehensive cataloguing system. Over centuries, successive Lobkowicz princes enriched the collection, reflecting their political, cultural, and scholarly engagements. Confiscated during World War II and nationalized under the communist regime, the library was returned to the Lobkowicz family in 1992. Today, the library is housed in Nelahozeves Castle. From 1657 until 1942, the library was located at the family’s ducal residence in Roudnice nad Labem. Throughout the 19th century, the library was reorganized, inventoried, and recorded in a handwritten catalogue, which remains the only existing inventory of the collection until today. Only selected parts of the library (e.g., incunabula, Spanish and Italian prints) have been published in printed catalogues.