Birds have long held a unique dual role as a model group for scientists and as the focus of birders' passionate quests. Despite centuries of observation, each year brings the discovery and description of several entirely new avian species and hundreds of other taxonomic "splits" or "lumps" based on DNA data. In this arena of continual and increasing taxonomic change, The Clements Checklist presents the most up-to-date and most widely endorsed compendium of the more than 9800 species of birds recognized by the scientific and birding communities. This completely revised sixth edition is current as of January 1, 2007, and incorporates hundreds of updates since the last edition. In taxonomic sequence, it provides the scientific and English name of each species and a description of the worldwide range of each species and subspecies. The most established resource on the taxonomy and biogeography of birds for the world birding community, The Clements Checklist is the official world checklist of the American Birding Association (ABA) and is used as the authoritative reference in the birding competitions and listing activities of this preeminent North American organization for serious birders. Features of The Clements Checklist include: *comprehensive indexes with all taxa listed by English and scientific names; *tables and maps showing the world distribution of total bird species and endemics by geographic area, which will be of special interest to conservationists; and *space to record the location and date of individual sightings, providing the user with a personalized ornithological journal. The checklist is being continually updated by the Cornell Laboratory of Ornithology. These updates are being posted to the Lab's website evey three months and will eventually be incorporated into the next edition of The Clements Checklist.