This book constitutes the thoroughly refereed postproceedings of the Second International Symposium on Ubiquitous Computing Systems, UCS 2004, held in Tokyo, Japan in November 2004.

The 20 revised full papers including 2 invited papers presented were carefully reviewed and selected from 50 submissions for inclusion in the book. The emerging research area of ubiquitous computing systems is an outcome of the rapid evolution in smart appliances and devices, as well as tremendous advances in wireless networks and mobile computing. The topical sections covered are location-aware computing, real-world interaction, systems, context awareness, and sensors and tags.