This paper summarizes research leading to the development of acomprehensive constitutive modeling approach for granular bases,subbases, and subgrade soils. The model that was developed isbased on the flow theory of plasticity. It rationally considersboth the resilient and permanent deformation response, and accountsfor the effects of repeated loading and saturation and drainageconditions. The model can be used to predict pavement performance,to select pavement layer thicknesses to resist permanent deformations,and to select material properties to assure adequate performance.This paper describes the conceptual model development. It alsopresents results from a laboratory evaluation of the constitutivemodel using three materials covering the range of materials typicallyclassified as granular in pavement construction. Finally, themodeling concepts are applied to practical pavement design problems.