This paper describes software that examines and reacts to an individual's changing context. Such software can promote and mediate people's interactions with devices, computers, and other people, and it can help navigate unfamiliar places. We believe that a limited amount of information covering a person's proximate environment is most important for this form of computing since the interesting part of the world around us is what we can see, hear, and touch. In this paper we define context-aware computing, and describe four categories of context-aware applications: proximate selection, automatic contextual reconfiguration, contextual information and commands, and context-triggered actions. Instances of these application types have been prototyped on the PARCTAB, a wireless, palm-sized computer.