Many libraries, archives, and museums provide their users with social computing environments that include the ability to tag collections, annotate objects, and otherwise contribute their thoughts to the knowledge base of the institution. Information professionals have responded to the world of user-created content by developing open source tools to coordinate these activities and researching the best ways to involve users in the co-creation of digital knowledge. This rapid influx of new technologies and new methods for interacting with users comes at a time when libraries, archives, and museums still struggle to share data across their own institutions, let alone between institutions of different types. Information professionals had barely begun to make progress developing crosswalks and data interoperability standards when, as social computing became the norm on the Web, providing the ability for users to manipulate data changed from a cool toy to a basic expectation. Moving forward—and keeping pace with user expectations— requires the coordination of many different users (in all their variety) as they contribute, participate, shape, and create all types of data in all types of contexts. This issue of Library Trends offers the chance to consider what social computing means for the future of libraries, archives, and museums, and to think carefully about the future trends and long-term implications of involving users in the co-construction of knowledge online. The authors of the following articles have thought broadly about the issues raised when we bring users into the mix in various ways and at various points in the information life cycle. Their efforts contribute to ongoing broad-based discussions about what happens when users are involved in shaping, guiding, and directing the development of online libraries, archives, and museums and their information resources.