In the eighteenth century, the entomologist and industrialist Charles de Geer (1720–1778), who spent his formative years in the Netherlands, established a library in his manor at Leufstabruk. Since 1986 this library has been owned by Uppsala University Library. This volume contains essays on different aspects of this historical book collection, as well as of similar country house libraries in Sweden and abroad. It is the result of an international symposium held in Leufstabruk and Uppsala in June 2022.