Vendémiaire (French pronunciation: ​[vɑ̃demjɛʁ]) was the first month in the French Republican calendar. The month was named after the Occitan word vendemiaire (grape harvester).

Vendémiaire was the first month of the autumn quarter (mois d'automne). It started on the day of the autumnal equinox, which fell between 22 September and 24 September, inclusive. It thus ended between 21 October and 23 October, and was the season of the vintage in the wine districts of northern France. It follows the Sansculottides of the past year and precedes Brumaire.