This book constitutes the refereed proceedings of the 9th International Conference on Ubiquitous Computing, UbiComp 2007, held in Innsbruck, Austria, in September 2007.

The 29 revised full papers presented were carefully reviewed and selected from 150 submissions. The papers address all current issues in the area of ubiquitous, pervasive and handheld computing systems and their applications including topics like: tools and techniques for designing, implementing, and evaluating ubiquitous computing systems, mobile, wireless, and ad hoc networking infrastructures for ubiquitous computing, laboratory and in situ studies of ubiquitous computing technologies in use, location-aware and context-based systems for ubiquitous computing, privacy, security, and trust in ubiquitous and pervasive systems.