This book constitutes the refereed proceedings of the 4th International Conference on Ubiquitous Computing, UbiComp 2002, held in Goteborg, Sweden in September/October 2002. The 15 revised full papers and 14 technical notes presented were carefully reviewed and selected from a total of 195 submissions. The book offers topical sections on mobile and context-aware systems, user studies and design, perceptual interfaces and responsive environments, sharing and accessing information - public and private, location, and sensors and applications.