This high arid plateau is located at an altitude of more than 1,000 meters and stretches 50 to 60 km from east to west and 800 km from north to south, ie an area of nearly 120,000 km2. Over its entire surface are eroded rock formations emerging from sand dunes, reminiscent of the ruins of ancient cities.
Tassili n'Ajjer rises to 2,158 meters above sea level at Adrar Afao and emerges in high cliffs at an average of 1,500 meters above the ergs of Mourzouq and Oubari in the east and Admer in the Ténéré in the south. To the north, this high plateau is lost in the dunes of Issaouane and Bourharet.
The massif is inhabited by the Tuaregs of the Kel Ajjer group. Its main town is Djanet, a small oasis located on the western edge of the region.