Environmental informatics (or Enviromatics) is a subject with interdisciplinary roots in computer science, environmental planning, ecology, economics and other related areas. Its practitioners must be prepared to work with many diverse professional groups. It forms the foundation for computer-assisted environmental protection. This book contains an edited version of papers presented at the 3rd International Symposium on Environmental Software Systems (ISESS '99), which was held at the University of Otago, Dunedin, New Zealand, from August 30 to September 2, 1999, and was sponsored by the International Federation for Information Processing (IFIP). The text is divided into six sections: enviromatics introduction; environmental issues; environmental information systems - tools and techniques; environmental information systems - implementations; environmental decision support systems; and specialized topics.