This chapter provides a high-level view of the key themes, current position and challenges of digital libraries and their technologies, social aspects, collections and communities. It begins by identifying the key themes of the second decade (2002-2012) of progress in the diverse, multidisciplinary, international field of digital libraries. A concept map visualizes the results of an analysis of second-decade digital library literature. The map provides new insights into this complex field by exposing thematic connections between technologies, collections, social forces and online community building. The chapter concludes with a consideration of key challenges facing digital libraries: interoperability, community engagement, intellectual property rights, and sustainability.