IntroductionSince its inception, the rationale underpinning environmental impact assessment (EIA) has been to provide an analysis of the potential significant environmental effects associated with major development proposals, and to communicate this information to decisionmakers and the wider public. The significance of environmental effects has long been identified as the most critical element of EIA (Duinker and Beanlands, 1986;Sadler, 1996), with impact assessment legislation, guidelines, and Environmental Impact Statements (EISs) making liberalöif somewhat nebulousöuse of the term. There are now over 100 EIA systems in existence worldwide (Wood, 2003) and EIA regulations have been in operation for over fifteen years in the United Kingdom, where around 600 EISs are now produced annually. (1) EIA may therefore be considered to be approaching maturity, and yet in spite of a substantial body of experience, our knowledge of the use and meaning of the central concept of`significance' remains surprisingly rudimentary.Since the foundation of modern EIA in the United States under the National Environmental Policy Act of 1969, the classic model of normative decisionmaking underpinning the EIA process has centred on the assumption that environmental information will be employed in an instrumentally rational manner. In practice, although appearing to adopt a technical`scientific' approach to appraisal, the evaluation of the significance of environmental effects in EIA is ultimately dependent upon the specific environmental and social context, and is heavily reliant on professional and intuitive judgment and subjective decisions (