The refereed proceedings of the 4th International and Interdisciplinary Conference on Modeling and Using Context, CONTEXT 2003, held in Stanford, CA, USA in June 2003. The 31 full papers and 15 short papers presented were carefully reviewed, selected, and revised for inclusion in the book. The papers presented deal with the interdisciplinary topic of modeling and using context from various points of view, ranging through cognitive science, formal logic, artifical intelligence, computational intelligence, philosophical and psychological aspects, and information processing. Highly general philosophical and theoretical issues are complemented by specific applications in various fields.