What sets thriving, long-lived digital libraries apart from those that attract only modest attention or have faded into memory? Why have some digital libraries had a distinctive impact on the communities they were built to serve, while others are more or less ignored? This chapter of Exploring Digital Libraries examines these issues. It builds on table 2.1’s descriptions of a sample of working digital libraries that have been successful since they began in the first decade of digital libraries (1991-2001). It also takes up themes from chapter 6, which examines the ways that digital libraries produce, or could produce value for the communities they serve.