Welcome to the proceedings of the 2004 International Conference on Embedded and Ubiquitous Computing (EUC 2004) which was held in Aizu-Wakamatsu City, Japan, 25–27 August 2004. Embedded and ubiquitous computing are emerging rapidly as exciting new paradigms and disciplines to provide computing and communication services all the time, everywhere. Its systems are now invading every aspect of life to the point that they are disappearing inside all sorts of appliances or can be worn unobtrusively as part of clothing and jewelry, etc. This emergence is a natural outcome of research and technological advances in embedded systems, pervasive computing and communications, wireless networks, mobile computing, distri- ted computing and agent technologies, etc. Its explosive impact on academia, industry, government and daily life can be compared to that of electric motors over the past century but promises to revolutionize life much more profoundly than elevators, electric motors or even personal computer evolution ever did. The EUC 2004 conference provided a forum for engineers and scientists in academia, industry, and government to address all the resulting profound ch- lenges including technical, safety, social, legal, political, and economic issues, and to present and discuss their ideas, results, work in progress and experience on all aspects of embedded and ubiquitous computing. There was a very large number of paper submissions (260) from more than 20 countries and regions, including not only Asia and the Pacific, but also Europe and North America. All submissions were reviewed by at least three program or technical committee members or external reviewers.