The paper introduces some of the main features of the geomorphology of the Air Mountains, situated in the Niger Republic south of the Hoggar. The mountains are composed of granitic and metamorphic crystalline basement rocks which emerge through the surrounding Carboniferous to Cretaceous sediments and are overlain in places by end-Cainozoic lavas. An end-Cretaceous fault-trough extends into the heart of Air and, together with other evidence, indicates that the crystalline rocks were buried during the Cretaceous marine transgression. Geological and geomorphological evidence suggests deformation and uplift in end-Cretaceous, end-Palaeocene and end-Tertiary-Pleistocene times. Discordant upon the crystalline and consequent upon the sedimentary rocks, the superimposed drainage pattern was initiated during the end-Cretaceous emergence. The relief consists of a deformed main Air planation surface at 6oo1000 m, surmounted by resistant granite massifs some of which are bevelled by a deformed, multiphase summit planation surface at 1400-I900 m. The main Air surface is also being dissected by an end-Tertiary-Pleistocene planation cycle 100-300 m lower than the main surface. The summit surface is either Cretaceous or Palaeocene in age and the main Air surface is Tertiary (post-Palaeocene). The morphology of the Timia Jurassic granite ring complex is described with special reference to the differential erosion of the various granites. The degree of erosion and relative rock resistance are both similar to those in the Nigerian massifs and it is concluded that Tertiary denudation in the two regions, the one now arid, the other humid, was similar. Evidence is presented which suggests that Tertiary climates in the southern Sahara may have been seasonally more humid than now. Pleistocene aggradational landforms are prominent in Air and indicate changes in geomorphological activity. The role of tectonics and climatic change in producing these variations is examined and it is concluded that climate is the most likely cause. Following J. Chavaillon, it is argued that the two, possibly three, phases of kori (wadi)incision and aggradation were produced during the opening and closing phases of pluvial periods. Correlation with other Saharan and Sudanic regions may suggest that the coarse material ('gravel') and 'sandy' terraces are related to the 'Aterian' 40,000-7000 BP and 'Neolithic' 5000-2400 BP pluvial periods respectively. This can be no more than a working hypothesis in view of the limited amount of research to date. The Air may form a valuable link in the interpretation of arid and humid west African landfornis and provides an interesting case study in Saharan geomorphology. THE PURPOSE of this paper is to present an outline of the geomorphology of a little-known region in the southern Sahara, emphasizing three of its salient morphological features. These are the planation surfaces and the evolution of Air, the morphology of the Jurassic granite massifs, and the Pleistocene aggradational landforms. While the evolutionary approach to landform analysis has received considerable criticism of late, the nature of the Air landforms and geology suggests that such an approach may be useful and valid, as has been demonstrated for the Hoggar Mountains, a similar region, by P. Birot, R. Capot-Rey and J. Dresch (I955). The remarkably resistant Jurassic granite ring complexes exhibit interesting relationships between their structure, lithology and relief in addition to being the most striking of the high mountains in Air. The Pleistocene deposits, together with the morphology of the Jurassic granites, throw light upon the morphoclimatic aspects of Air and add substance to the belief that the landscapes of the Sahara partly reflect denudation processes related to a moister Cainozoic era. The Air extends over 84,000 km2 in the Republic of Niger. It consists of crystalline rocks which emerge as a horst through the surrounding Palaeozoic to Tertiary sediments in the basins of the Tenere, Tamesna (Damergou) and Talakh (Fig. I). The general altitude of Air