Mobile phones and PDAs are converging into mobile lifestyle devices that offer a wide range of applications to end users. Many of these applications will have the ability to adapt themselves to the user’s situation, commonly referred to as context awareness. We argue that an infrastructure is needed to enable wide deployment of context-aware applications. A major benefit is interoperability between heterogeneous context sources and applications in a privacy-sensitive way. We identify three main technical challenges to realize such an infrastructure: • Reasoning to infer higher-level and better quality context information • Efficient exchange and distributed processing of context information in dynamic and pervasive environments • End-user-controlled handling of the privacy aspects This article explains how we address these challenges with regard to the realization of an infrastructure that supports context-aware mobile applications. We use this infrastructure to support several mobile healthcare applications.