A geological reconnaissance of the Beni Ulid — Wadi Merdum region of the pre-desert of Tripolitania shows that at least twenty, stratigraphically distinct geomorphic events can be recognised from field exposures, field mapping and the analysis of Spacelab metric camera photography. The earliest events are provisionally attributed to the early Cenozoic and include uplift, tilting, faulting, the formation of karstic and karst-tectonic landforms, and erosion by meandering river systems. Some of these valleys were infilled with lava flows from the south-south-west in the ?late Palaeocene/early Eocene. Re-excavation of the ancient landscape by rivers followed. Pleistocene deposits of powerful, often braided rivers occur in the wadi floor. The wadi sides are clothed in complex sequences of alluvial fans, screes, windblown, waterlain and anthropogenic deposits, sometimes with weathering horizons and calcretes of uncertain stratigraphic significance. The plateaux contain large alluvial basins, palaeosols, soils and weathering horizons of uncertain age. Accelerated soil erosion caused by human activity appears to have been important in the area — slope deposits of scree and midden between 4 and 8 metres in thickness have accumulated beneath one gasr during a 500 year period. The most recent deposits identified are complex aeolian deposits at the wadi edge and the interdigitating series of floodloams and aeolian sands on the wadi floors.