A mathematical basis for the development of constitutive drivers in soil plasticity has been proposed by the authors. A constitutive driver is here understood as a computer program, containing a number of selected constitutive models, in which different laboratory and field tests can be simulated and model parameters optimised. As a pilot study of the mathematical concept, a constitutive driver for soils, in the form of a PC-program, has been developed. The paper discusses this particular program, i.e. its structure, the mathematical basis, included soil models and some application examples, to give an idea of how a general and user-friendly constitutive driver can be designed. Such a program can be used for practical, research and educational purposes. In fact, it is believed that so many important applications for constitutive drivers exist that it would be beneficial if such programs were easily accessible as complementary programs in commercial software.