Geotechnical journals and conferences abound with constitutive models. The choice of model is to some extent a matter of mathematical aesthetics and subjective judgement. We cannot hope to describe all possible constitutive modelling proposals here. However, there are some models which have been so widely used that they are rather generally available in all numerical analysis programs that are intended for application to geotechnical problems: isotropic elasticity; elastic-perfectly plastic Mohr-Coulomb; and Cam clay. We will present not only these models but also modest developments from these models. Our thesis is that engineers are more likely to make use of models which can be clearly seen as incrementally different from models with which they have some familiarity than to make use of models which adopt a completely different language. Thus a hardening plasticity model will be presented which is an obvious and logical extension of the perfectly plastic Mohr-Coulomb model.