Platforms for social computing connect users via shared references to people with whom they have relationships, events attended, places lived in or traveled to, and topics such as favorite books or movies. This model needn't be limited to social networking sites. Understanding an item in a digital library or museum requires context: information about the topics, places, events, and people to which the item is related. Students, journalists and investigators traditionally discover this kind context by asking “the four Ws”: what, where, when and who. We are building open, distributed systems that allow users to ask and answer these questions via links to appropriate contextual resources.