A field and laboratory investigation of the slope stability of the Chalk is described. A review of previous work on rock slope stability and a working hypothesis based on the "state of the art" are presented. The engineering geology of the Chalk is reviewed. Natural and artificial slopes in chalk have been investigated and typical slope angles and types of failure recognised. Movements of the walls of experimental trial pits have been recorded and the causes of these movements are discussed. Two main types of slope instability have been recognised; slope degradation and major slope failures, fractures present within the Chalk are largely responsible for controlling the major failures. A regional analysis of the fracture pattern within the Chalk and its effect on slope stability are described. Measurements have been made of the spacing of fractures and geophysical methods used for in situ determinations. Different types of fracture surfaces have been recognised in the field and investigated in the laboratory. The effect of fracture surfaces on shear strength is discussed, and a simple sliding apparatus for testing fractures has been devised. A model is suggested for the development of slopes in chalk and the effects of the interacting factors which determine stability are discussed. Criteria are given which allow a practical approach to the design of new slopes and the assessment of existing slopes. Some suggestions are made for further work.