This paper proposes the concept of digital cities as a social information infrastructure for urban life (including shopping, business, transportation, education, welfare and so on). We propose the three layer architecture for digital cities: a) the information layer integrates both WWW archives and real-time sensory information related to the city, b) the inteTface layer provides 2D and 3D views of the city, and c) the interaction layer assists social interaction among people who are living/visiting in/at the city. We started a three year project to develop a digital city for Kyoto, the old capital and cultural center of Japan, based on the newest technologies including GIS, 3D, animation, agents and mobile computing. This paper introduces the system architecture and the current status of Digital City Kyoto.