Drawing upon new evidence and exploiting new modes of analysis, we set out what can be known at present about the great imperial libraries of Rome. We trace their origins through the various conceptions of Caesar, Varro, and Pollio, and show that the imperial libraries were a continuation of late Republican practice : emperors acquired substantial book collections, stored them in several different structures, embellished the buildings with works of art, and allowed friends, scholars, and others to use the volumes. We pay close attention to the sources of the books, the uses and users of the libraries, and the fires that ravaged them. We argue that there were no libraries in the imperial thermae and that there were at most five or six librar...