The IUCN Red List Categories and Criteria have undergone an extensive review in recent years. This review has produced a clearer, more open, and easy-to-use system. The revised Categories and Criteria (IUCN Red List Categories and Criteria version 3.1) were adopted by IUCN Council in February 2000 and all new assessments and reassessments of taxa on the IUCN Red List must follow this revised system.

The conversion of all existing assessments on the Red List to the revised system will take time. In the interim, the current Red List includes assessments using both the 1994 Red List Categories and Criteria and the 2001 Categories and Criteria. To avoid confusion, all assessments using the 2001 Categories and Criteria are indicated by a ' ver 3.1 (2001) ' hyperlink, and all assessments using the 1994 Categories and Criteria are indicated by a ' ver 2.3 (1994) ' hyperlink.

• 2001 IUCN Red List Categories and Criteria version 3.1. All new assessments and reassessments on the IUCN Red List use this system. Some assessments from 1996-2000 have also been converted to follow the revised categories and criteria. All of these are clearly indicated.

• 1994 IUCN Red List Categories and Criteria. Assessments from 1996-2000 that have not been converted over to the revised system, use the 1994 categories and criteria.