This book constitutes the refereed proceedings of the Third International Conference on Ubiquitous Computing, Ubicomp 2001, held in Atlanta, GA, USA in September/October 2001. The 14 revised full papers and 15 revised technical notes were carefully selected during a highly competitive reviewing process from a total of 160 submissions (90 paper submissions and 70 technical notes submissions). All current aspects of research and development in the booming area of ubiquitous computing are addressed. The book offers topical sections on location awareness, tools and infrastructure, applications for groups, applications and design spaces, research challenges and novel input, and output.