Privacy is the most often-cited criticism of ubiquitous computing, and may be the greatest barrier to its long-term success. However, developers currently have little guidance or programming support in creating useful and usable interactions that are effective in helping end-users manage their privacy. To address this problem, we present Context Fabric, an infrastructure for facilitating the development of privacy-sensitive ubiquitous computing applications. The requirements for Context Fabric were gathered through an analysis of end-user needs and application developer needs for privacy. Context Fabric provides basic support for building ubiquitous computing applications, providing several customizable privacy mechanisms as well as a framework for extending privacy functionality. These mechanisms facilitate the creation of three basic interaction patterns for privacy-sensitive applications: optimistic, pessimistic, and mixed-initiative. Combined, these features allow application developers and end-users to support a spectrum of trust levels and privacy needs.