This thesis investigates public access to environmental information, starting with the examination of environmental information and environmental information systems (EIS). This examination demonstrates that term “environmental information” holds a wide range of meaning, and while it is possible to describe “core environmental information”, the full range of environmental information is open for wide interpretation. In regard to environmental information systems, the thesis demonstrates the importance of Geographical Information Systems (GIS) as a major component of most EIS, and the influence of the institutional settings within which they operate on these systems. To better understand the requirements and needs of likely users of environmental information (those with interest in environmental issues and with access to the technology), the thesis contains two empirical studies – a web-based survey of requirements and needs from a public environmental information system for London, and a public participation workshop in which representatives of local interest groups explored the use of GIS for local planning purposes. The analysis of these studies (using the framework of Soft Systems Methodology) leads to the development of conceptual models and criteria set for public access to environmental information. These models and criteria are then compared to existing web-based information systems, a comparison that reveals gaps between the desired system and the current state of the art. The thesis ends with some suggestions about how to improve information systems to improve public access. The thesis is based upon a wide array of topics, including aspects of Human-Computer Interaction (HCI) in the context of Geographical and Environmental Information Systems (GIS/EIS). Information Systems Design methodologies, Public Participation GIS (PPFIS), Public Understanding of Science (PUS), social aspects of Information and Communication Technologies (ICT) and Philosophy of Technology.