Recent developments in wireless communication, mobile computing, and sensor technologies have prompted a new vision of the world in which we live. As witnesses the effects of Moore's law, which are evident in many aspects of innovative technical opportunity, such as cost, size, capacity, bandwidth, etc. These advances allow us to build new types of human-computer-environment interaction in augmented physical spaces. Ideally, mobile computing devices can go with people so that they can access information on the move as being constantly connected to the digital space. Sensor technologies enable mobile computing devices to sense their users and environments. This increases the interaction bandwidth between a human and a mobile computing device. The development of context-sensitive mobile computing systems requires considerable engineering skills. None of the existing approaches provides an effective means of obtaining location and environmental information using "standard" hardware and software. This raises the entry level of discovering more about this type of interaction to the designers. In addition, it is important to stress that relatively little is known about the usability problems that might arise from interaction with these different context-sensitive mobile computing applications. The focus of this thesis is on the development of a prototyping environment for context-sensitive mobile computing. This thesis makes two contributions. The most significant contribution is the presentation of the Glasgow Context Server (GCS). It has been specifically designed to address the concerns mentioned above. It successfully integrates an off-the-shelf radio Local Area Network (LAN) with the infrared sensors that have been a feature of many previous context-sensitive mobile computing applications. The GCS is intended to help interface designers validate the claimed benefits of location sensing, location disclosing and environment sensing applications. The second contribution is the working applications, in particular, a web-based annotation system for physical objects and a shopping assistant built upon the GCS environment. These demonstrations are used to evaluate the GCS approach and point out the challenging issues in computing technology as well as usability concern. The hope is that this research can provide interface designers with an in-depth reference to a prototyping environment for context-sensitive mobile computing applications.