This article explains the fundamental concepts of Internet geographic information system (GIS) technology and illustrates its capabilities using the example of water quality monitoring in San Diego Bay Watershed, California. Internet GIS technology has democratized public access to geographic data and information services, and software applications such as Google Earth provide millions of users with instantaneous access to digital geographic data and tools that, until recently, were only available to GIS specialists. In addition to making geographic data accessible to a large number of potential users, Internet GIS is also a technological vehicle for encouraging public participation in local decision-making processes. Key developments of Internet GIS technology are highlighted. The links between Internet GIS and public participation are summarized and an application called Common Ground is described. Common Ground delivers data and information about water quality in the San Diego Bay Watershed to the public. The design, architecture, and capabilities of this Internet GIS application are discussed, and the lessons learned and the outlooks for future Internet GIS developments are evaluated.