The book describes experimental observations and principles of mechanics, and efficient computational algorithms for stress calculations as typically performed in finite element analysis. The theoretical background is given to an extent necessary to describe the commonly employed material models in metal isotropic and orthotropic plasticity, thermoplasticity and viscoplasticity, and the plasticity of geological materials. The computational algorithms are developed in a unified manner with some detailed derivations of the algorithmic relations. Many solved examples are presented, which are designed to give insight into the material behavior in various engineering conditions, and to demonstrate the application of the computational algorithms.