In the geologic timescale, the Sinemurian is an age and stage in the Early or Lower Jurassic Epoch or Series.

The Sinemurian Stage was defined and introduced into scientific literature by French palaeontologist Alcide d'Orbigny in 1842.

The calcareous soil formed from the Jurassic limestone of the region is in part responsible for the character of the classic Sancerre wines.

The base of the Sinemurian Stage is at the first appearance of the ammonite genera Vermiceras and Metophioceras in the stratigraphic record.

A global reference profile (GSSP or golden spike) for the Sinemurian Stage is located in a cliff north of the hamlet of East Quantoxhead, 6 kilometers (3.7 mi) east of Watchet, Somerset, England.