The A66 autoroute is a 38.2 kilometres (23.7 mi) long motorway in the south of France, also called L'Ariégeoise.

It is in the departments of the Haute-Garonne and Ariège, and connects Villefranche-de-Lauragais with a junction to the A61 at its north and ends at the N20 at Pamiers to the south.

It forms part of a larger European route which connects Paris, Orléans, Limoges, Toulouse, and Barcelona.

The road provides access to the Midi-Pyrénées towards the Principality of Andorra, and the junctions between Ariégeois and Toulouse.

The following exchangers are now on the RN20, but a number is still allotted to them: The N20 dual carriageway between Pamiers, Foix and Tarascon-sur-Ariège is to be upgraded to motorway standard, and renumbered the A66, however no date for this has been announced.