Introduction Impact assessment originated with a desire for profound change in both the philosophy and the methodology of resource management. Common to all forms of impact assessment is 'an assumption that a systematic, focused, interdisciplinary use of science may improve the quality of planning and decision-making' (Caldwell, 1988a: 75). This tenet first found expression with the passage in the United States of the National Environmental Policy Act (NEPA) in 1969, reviewed in Chapter l.