The Phanerozoic (Brit. Phanærozoic) is the current geologic eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared. Its name derives from the Greek words φανερός and ζωή, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon. The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean and Proterozoic eons.

The time span of the Phanerozoic includes the rapid emergence of a number of animal phyla; the evolution of these phyla into diverse forms; the emergence of terrestrial plants; the development of complex plants; the evolution of fish; the emergence of terrestrial animals; and the development of modern faunas. During the period covered, continents drifted about, eventually collecting into a single landmass known as Pangaea and then splitting up into the current continental landmasses.