This book introduces the SMP criterion, the integration of the SMP criterion with the well-known Cam-clay model, and the application of the SMP criterion to the general elastoplastic constitutive models for geomaterials like clay, sand and unsaturated soil. The SMP failure criterion is the most reasonable three-dimensional extension of the Mohr-Coulomb failure criterion from the point of view of its physical meaning, mathematical expression and geometrical presentation. The Cam-clay model is a fundamental constitutive model in soil mechanics, but is only suitable for normally consolidated clay under triaxial compression stress states. Therefore, to integrate the Cam-clay model with the SMP criterion and extend it to sand and other geomaterials is one of the fundamental tasks in geotechnical engineering. In addition to the theoretical development of constitutive models, the book is full of high-quality experimental data obtained from conventional and true triaxial tests on various soils. The scope and the level of the book ensure that it will be a valuable resource for postgraduate students, academics and geotechnical engineering professionals alike.