Social web services catalog users' activities across the Internet, aggregating, analyzing, and selling a vast array of user data to be used largely for consumer profiling and target marketing. This article interrogates the tacit agreements and terms-of-use policies that govern who owns user data, how it circulates, and how it can be used. Relying on problematic assumptions about the authorship of social data, data-mining practices and technology policies unquestioningly place ownership in the hands of technology companies and compel users to surrender control over their own contributions on the social web. This article explores the implications of the practices and policies surrounding data management for composition and participation on the social web and argues for a more balanced distribution of rights to user data. (Contains 2 notes.)