The Cenozoic Era ( /ˌsɛnəˈzoʊ.ɨk/ or /ˌsiːnəˈzoʊ.ɨk/; also Cænozoic or Cainozoic; meaning "new life", from Greek καινός kainos "new", and ζωή zoe "life") is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 65.5 Ma to the present.

The era began in the wake of the Cretaceous–Paleogene extinction event (K-Pg event) at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs (as well as other terrestrial and marine flora and fauna) at the end of the Mesozoic. The Cenozoic is also known as the Age of Mammals, because the extinction of many groups allowed mammals to greatly diversify.

Early in the Cenozoic, following the K-Pg event, the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. Some birds grew larger than the average human. This group became known as the "terror birds," and were formidable predators. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's mammals.