For 2000 years the state-run libraries of imperial China systematically assembled standard collections of books from the past and present. Although the collections themselves were lost through warfare and fire, the classified catalogues prepared by the Privy Director of Books were often used in compiling national bibliographies for the state-sponsored dynastic histories. Through these and other catalogues we learn much about books now lost and even the contents of lost books can be sampled through quotations in medieval encyclopedias. These lectures discuss the dynamics of loss and survival; the role of the imperial state in manipulating book culture through classification and selective preservation; the significance of lost books as an index of superseded knowledge and values. An analysis of two specific cases demonstrates the insights to be gained through textual reconstruction and the inadequacies of standard classifications in times past and present. Medieval Chinese literature emerges as a richer, more problematic, less docile body of work than the orthodoxies of the last millennium would wish.