The IUCN (International Union for Conservation of Nature) has recently issued an updated version of its well-known IUCN Redlist, the most comprehensive and authoritative measure of the endangered-ness of species around the world. According to the latest information, 17,291 species are threatened with extinction out of a total of 47,677 assessed species. "The scientific evidence of a serious extinction crisis is mounting,” according to Jane Smart, Director of IUCN’s Biodiversity Conservation Group.
Below are some graphs, illustrating the most recent statistics. Red areas represent species that are threatened. One thing to keep in mind while looking at these charts--these graphics represent only species that are assessed by the IUCN. So, although just about all of the known mammal, amphibian, and bird species have been described and assessed, only small percentages of the world's known plants, invertebrates, fish, and reptiles, have been assessed. Which of course means that there are a lot of species out there whose status is unknown. They may be threatened or not--we just don't know. If you're interested in more details, check out the Summary Statistics published by the IUCN.