The Otoyol is the national network of controlled-access highways in Turkey. The term Otoyol translates to motorway while the literal meaning is auto-route. The Otoyol was first opened in 1973.

Otoyol 21, abbreviated as O-21, a.k.a. Ankara-Tarsus Otoyolu, is a completed toll motorway in the Central Anatolia and Mediterranean regions in Turkey. Currently, it is connecting Otoyol 20 from Gölbaşı, Ankara with the Adana-Mersin Motorway O-51 at Tarsus in Mersin Province. On its full length, it is part of the European E90. The last part of the highway opened on 16 December 2020.