This chapter deals with the magnitude and distribution of lateral pressure between a soil mass and an adjoining retaining structure. Conditions of plane strain are assumed, i. e. strains in the longitudinal direction of the structure are assumed to be zero. The rigorous treatment of this type of problem, with both stresses and displacements being considered, would involve a knowledge of appropriate equations defining the stress–strain relationship for the soil and the solution of the equations of equilibrium and compatibility for the given boundary conditions. It is possible to determine displacements by means of the finite element method using suitable computer software, provided realistic values of the relevant deformation parameters are available. However, it is the failure condition of the retained soil mass which is of primary interest and in this context, provided a consideration of displacements is not required, it is possible to use the concept of plastic collapse. Earth pressure problems can thus be considered as problems in plasticity.