An alternative to elastoplastic models for the mathematical description of soil mechanical behaviour appeared in 1977, created by KOLYMBAS in his doctoral thesis at the University of Karlsruhe, Germany, and was named hypoplasticity. The article present the basic concepts of the hypoplastic constitutive model for the behaviour of granular materials. With a single constitutive equation, inspired by modern rational mechanics, without recorurse to yield or potential surfaces, important phenomena of soil mechanical behaviour can be represented. The development of the model is commented briefly.