UrbanWeb is a novel Web-based context-aware hypermedia plat-form. It provides essential mechanisms for mobile social comput-ing applications: the framework implements context as an exten-sion to Web 2.0 tagging and provides developers with an easy to use platform for mobile context-aware applications. Services can be statically or dynamically defined in the user’s context, data can be pre-cached for data intensive mobile applications, and shared state supports synchronization between running applications such as games. The paper discusses how UrbanWeb acquires cues about the user’s context from sensors in mobile phones, ranging from GPS data, to 2D barcodes, and manual entry of context in-formation, as well as how to utilize this context in applications. The experiences show that the UrbanWeb platform efficiently supports a rich variety of urban computing applications in differ-ent scales of user populations.