This research proposes an on-line Environmental Information System for Planners (EISP). The Environmental Information System for Planners has been developed in collaboration with five local authorities as a web-based system designed to support decision making within the UK planning framework. It has been built as a ‘proof-of-concept’ system to demonstrate the value to urban planning of making information on environmental issues more widely accessible. The EISP has been designed to support three principal planning functions carried out by Local Authorities: Pre-planning enquiries; Development control decisions; and Strategic planning. The system incorporates 12 environmental themes: Air quality (PM10); Shallow undermining; Landslide susceptibility; Groundwater protection; Flood risk; Drainage; Land contamination; Proximity to landfill; Biodiversity; Natural heritage designations; Man-made heritage; and Natural Ground Stability (Geohazards). The design framework is based upon a series of decision flow diagrams, each covering one of the above themes. These decision flows take account of current planning procedures in the UK. Industry-standard web technologies have been employed to integrate the flows and develop the functionality that will allow the planner access to the system through secure web pages. Underpinning the system is an environmental Geographical Information System (GIS) that contains the most up-to-date data, information and models relevant to each of the environmental themes listed. The planning regulations are subject to change and so the system has been designed in a modular way so that new legislation can be accommodated without the need for a complete system rewrite. This modular approach also means that the system can be readily adapted to reflect local priorities and to draw on local datasets. The EISP was successfully tested and the thesis concludes with a costed business case study for commercial implementation and rollout of a production EISP system populated with appropriate environmental data within UK local authorities.