The Holocene extinction is the widespread, ongoing extinction of species during the present Holocene epoch. The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods; a sizeable fraction of these extinctions are occurring in the rainforests. Between 1500 and 2009, 875 extinctions have been documented by the International Union for Conservation of Nature and Natural Resources.^[1] However, since most extinctions go undocumented, scientists estimate that during the 20th century, between 20,000 and two million species actually became extinct, but the precise total cannot be determined more accurately within the limits of present knowledge. Up to 140,000 species per year (based on Species-area theory)^[2] may be the present rate of extinction based upon upper bound estimating.

In broad usage, Holocene extinction includes the notable disappearance of large mammals, known as megafauna, starting 10,000 years ago as humans developed and spread. Such disappearances have normally been considered as either a response to climate change, a result of the proliferation of modern humans, or both; however in 2007 a cometary impact hypothesis was presented, but has not been broadly accepted. These extinctions, occurring near the Pleistocene-Holocene boundary, are sometimes referred to as the Quaternary extinction event or Ice Age extinction. However the Holocene extinction may be regarded as continuing into the 21st century.

There is no general agreement on whether to consider more recent extinctions as a distinct event or merely part of the Quaternary extinction event. Only during these most recent parts of the extinction have plants also suffered large losses. Overall, the Holocene extinction is most significantly characterised by the presence of human-made driving factors and climate change.