This chapter explores the potential benefits and costs of the involuntary mass digitization of millions of printed books contained in the libraries that join the Google Books project. The ability to search for and preview relevant passages in copyrighted books may expand the potential market for the books, which might otherwise be obscure. Limited time, personnel, and shelf space mean that that many books will go unnoticed. Full-text search of digitized books may increase sales by exposing passages to more readers, courts have found, just as the dissemination of trailers, plot overviews, and frames from films and video games may increase the viewership and acquisition of them. On the other hand, authors and publishers are concerned that a Napster for books may result in the leakage of scans to the Internet, and the loss of an opportunity to license inclusion in digital libraries and derivative works. The chapter therefore provides an overview of the economics of fair use and derivative works, as well as of sampling and widespread digital infringement, before analyzing the courts’ fair use findings as to Google Books and a related project, HathiTrust.