Biodiversity has emerged as a prominent issue in the scientific and conservation communities, and is of increasing concern to the general public. As with other 'new' environmental problems (e.g., global climate change, stratospheric ozone depletion), biodiversity is difficult to evaluate because it involves slow, cumulative, complex effects that are unquestionably serious but difficult to document. Unlike 'traditional' pollution concerns, these new problems are not confined to one location or tied to one development or industry but are regional or global in scope. Given scientific uncertainty about cause-effect relationships, it is very difficult to formulate environmental policy or regulations that adequately address the problem. Biodiversity is also a very broad issue, involving aspects of species richness, species composition, genetic variation, habitat structure, landscape pattern, and ecological and evolutionary processes. Although components of biodiversity are addressed by various pieces of environmental legislation, a comprehensive approach is lacking. A new interpretation of the National Environmental Policy Act (NEPA) could involve the recognition of particular attributes or 'indicators' of biodiversity to address in the environmental assessment and review process. A hierarchical framework of compositional, structural, and functional biodiversity from which measurable indicators can be selected, is presented.