The Triassic is the first geological period in the Mesozoic era and the seventh period of the Phanerozoic eon. It lasted 50.6 million years. The period began 251.9 million years ago, and ended 201.3 million years ago.

The period before the Triassic was the Permian period, the last period in the Palaeozoic era. The Jurassic period came after the Triassic.

Many new groups arose during the Triassic period, including the dinosaurs and the first mammals.