Permian organisms lived during the Permian period, which extended from about 299 to 251 million years ago, for a total length of roughly 48 million years. The period opened with an era of glaciation similar to the relatively recent Ice Ages of modern geologic times, then warmed up midway through the period. Sea levels rose accordingly, producing large continental seas friendly to marine life. The Permian era ended with the most severe mass extinction in the history of life, the end-Permian extinction, which wiped out 95% of marine genera and 70% of terrestrial genera. The Permian is also the last period of the Paleozoic era.

The supercontinent of Pangaea formed during the Permian, locking up all the continental landmasses in the world except for a microcontinent about half the size of Australia called South China. This large landmass caused the interior of the supercontinent to be extremely dry, while terrestrial animals spread all over it. The continent of Pangaea straddled the equator and had a rough C-shape.

The marine invertebrates of the Permian were mostly extensions of lines that originated in the mid and late Carboniferous period immediately before. These included the ever-present brachiopods, bryozoans, echinoderms, mollusks, corals, ammonoids, and others. Only one group of trilobites hung on until this period, only to become extinct at its conclusion. Marine vertebrates included numerous fishes, sharks, conodonts, and other animals that evolved during the Devonian, Carboniferous, and Cambrian respectively. The euryptids, huge sea scorpions that ruled the sea floors of almost the entire Paleozoic, finally went extinct at the end of the Permian.

In terms of terrestrial life, the Permian was a time of rapid evolution and change. The swamp-loving lycopods (a genus of clubmosses) were replaced by conifers, which could better adapt to the changing climate and had superior defenses against newly-evolved terrestrial herbivores.

The Permian was a time of great evolution for terrestrial animals. Insects diversified from their primitive state during the Carboniferous, producing many groups we find familiar today, such as scorpionflies, dragonflies, true bugs, wasps, and many others. The Permian has been called the greatest period of all time for the diversification of insects.

The Permian saw the first major diversification of amniote (non-amphibian) tetrapods, including competition between sauropsids (reptiles) and synapsids (the ancestors of mammals). Though many large amphibians existed throughout this period, they were joined by other large tetrapods, most notably the pelycosaurs, a sauropsid which had evolved in late Carboniferous and had their heyday during the Permian. In the late Permian, early archosaurs evolved, which would later give rise to the dinosaurs that would dominate the Mesozoic.

In the middle Permian, primitive therapsids (a mammalian ancestor) such as Dinocephalia evolved, and in the late Permian, more advanced therapsids such as gorgonopsians and dicynodonts evolved. The therapsids ranged in size from small rats to ox or bear-sized animals, while the pelycosaurs were usually large, between about 1 m (3.2 ft) to 4 m (13 ft) in size.

At the end of the Permian, most animals of every type died, and evolution had to start over with what few survivors were left, notably the pig-sized herbivorous therapsid Lystrosaurus