This article uses both actor network theory (ANT) and activity theory to trace and analyze the ways in which both Twitter and third-party applications support the development and maintenance of meaningful contexts for Twitter participants. After situating context within the notion of a ‘‘fire space’’, the authors use ANT to trace the actors that support finding and moving information. Then they analyze the ‘‘prescriptions’’ of each application using the activity-theory distinction between actions and operations. Finally, they combine an activity-theory analysis with heuristics derived from the concept of ‘‘findability’’ in order to explore design implications for Social Web applications.