AbstractA brief introduction to environmental impact assessment (E.I.A.) is given. An E.I.A. requires, as a final stage, the aggregation of diverse and highly subjective impacts, though in practice this is often done implicitly. Explicit aggregation techniques have their origins in cost-benefit analysis or decision analysis, and the appropriateness of these two techniques for applications in E.I.A.s is considered.An illustration of decision analysis is given in which multi-attribute value analysis is used to assist in the siting of new mines. The method can be presented as a development of the simple visual sieving technique, and by employing colour graphics facilities and microcomputers, a portable, flexible and powerful decision aid emerges: but powerful tools require careful handling.