There are eight categories in the new system. The first priority in compiling this present edition of the Red List was to assess all known mammal species, the second was to re-assess all other vertebrates in the 1994 Red List, the third was to cover the invertebrate groups in the 1994 Red List for which an active IUCN Specialist Group exists. These goals have been achieved. However, it is recognised that these criteria do not always lead to equally robust assessments of extinction risk, which depend upon the life history of the species. Many of these species have high potential for population maintenance under high levels of mortality, and such species might form the basis for fisheries.
Distribution is recorded in terms of country names.
Unless geographically very remote from each other, islands and other territories are included with the parent country. Most marine species also have distribution recorded in terms of standard FAO Marine Fishery Areas. Note that species without a country range in the database will not be retrieved through a country search in the database. Geopolitical events during recent years may have led to some inconsistency or errors in the distribution information provided. Within reasonable limits every effort has been made to determine which of the new nations that were part of the former Czechoslovakia, Yugoslavia and USSR support species previously attributed to the larger unit.