The progressive retreat undergone by natural slopes subject to weathering was investigated in the book. A reasonable estimate of crest retreat rates is of paramount importance to evaluate the design life of buildings, roads, railways, nuclear waste deposits and any construction located on the top of cliffs subject to weathering. Two methods were used in the modelling: an analytical one, based on the limit analysis upper bound method and a numerical one, based on the distinct element method. The obtained results were compared with published data from some monitored slopes showing a good match between experimental observations and predictions. When the soil strength and the weathering law are known, the model is able to predict the future evolution of cliffs in terms of both forefront geometry and crest retreat ? time relationship. Tables of results are also presented to provide geotechnical engineers and geologists with a simple and practical design tool.