Thinly surfaced pavement deflect principally because of strains in the soil and granular layers. These strains are due to both resilient and permanent effects. By means of a Eeuropean Union funded co- operative research project between several pavement research centres, the testing, characterisation and model implementation of the non-linier resillient and permanent behaviour of project briefly discussing the problems of obtaining representative laboratory data from repeated load triaxial tests, the formulation and applicability of material models, the inportance of non linearity and its implementation info finitie element non-linier analytical tools. Ilustrative data is presented and the overall approach provides a cogent means of assesing, describing and predicting the behaviour of the soil and unbound materials in pavement constructions.