Biological concepts basic for environmental policies are discussed, such as biodiversity (based on the notion of variety), conservation, ecosystem resilience, fragility ad disturbance, accumulative effects and cautionary principle. We analyze two main tools for conservation decisions, i.e., priority areas for conservation of biodiversity and lists of threatened species (which have been, in the practice of licensing, the only criterion taken into account). We also detail minimum criteria in protocols for environmental studies: taxonomic (all groups should be sampled), spatial (including the project area and those affected by it) and temporal (at least three annual cycles) coverage, whose sufficiency should be tested through accumulation curves Legislation concerning caves is used as an example.