The Central Clay Plain is situated between latitudes 16° and 10° North and longitudes 32° and 37° East, in the Republic of the Sudan. The parent materials of the clay soils which cover almost this entire area belong to two broad groups: alluvial, deltaic and paludal sediments from rivers belonging to the Nile system (aggradational clay plains), and colluvio-alluvial deposits derived from local rock weathering, pediplanation and short-distance transport (degradational clay plains). The soils are classified as Vertisols in three international systems. Relationships between soil parent material, landform, climate, vegetation and soils were defined in the field. Field studies were supported by an analysis of mineralogical, chemical and physical soil data. The various landscapes that together make the Central Clay Plain were delineated on a 1:2 000 000 pedogeomorphic map. Hypotheses on the sedimentation history of the aggradational plains were tested against data on geology, palaeoclimatology and palaeobotany in the literature. Soils, vegetation and landforms show the degradational plains to be pediplains in an advanced stage of planation. Special attention is given to soil classification, soil genesis, the process of pedoturbation, and the origin and impact of relatively small differences in soil morphology. It was found that the climatic north-south gradient has a stronger influence on soil properties than differences in parent material between aggradational and degradational plains.