The Clay-with-flints Formation outcrops on the high chalk plateaux and interfluves of the chalk downs in southern England. Both current and historical definitions of the clay-with-flints are detailed and important distinctions are identified with other deposits which appear identical but are formed in different ways. Historically pedological or geomorphological studies have been carried out on the deposit. Engineering studies are only carried out where the deposit is crossed by infrastructure. The physical and chemical processes acting on the deposit and the resulting effects on the physical properties are discussed.