This book constitutes the refereed proceedings of the Second European Symposium on Ambient Intelligence, EUSAI 2004, held in Eindhoven, The Netherlands in November 2004. The 36 revised full papers presented were carefully reviewed and selected from 90 submissions. The papers are organized in topical sections on ubiquitous computing: sofware architectures, communication, and distribution; context sensing and machine perception; human computer interaction in ambient intelligence environments; and algorithms, ontologies, and architectures for learning and adaptation.