Neogene Period: A unit of geologic time consisting of the Miocene, Pliocene, Pleistocene, and Holocene epochs. The Neogene Period follows the Paleogene Period and is ongoing. Previously Neogene ended with the beginning of Quaternary, but Quaternary is no longer recognized as a period of time. The terms 'Neogene System' and 'Upper Tertiary System' have also been used to describe what is currently called the 'Neogene Period'. The somewhat confusing terminology seems to be due to attempts to deal with the comparatively fine granularity of time units as time approaches the present and more information is preserved. By dividing the Cenozoic era into two 'periods' instead of 7 'epochs', the periods are more closely comparable to the duration of 'periods' in the Mesozoic and Paleozoic eras.

The Neogene covers roughly 26 million years. During the Neogene mammals and birds evolved considerably. Most other forms were relatively unchanged. Some continental motion took place, the most significant event being the connection of North and South America in the late Pliocene. Climates cooled somewhat over the duration of the Neogene culminating in continental glaciations in the Quaternary Era that follows.