The Mohr-Coulomb (MC) failure criterion is a set of linear equations in principal stress space describing the conditions for which an isotropic material will fail, with any effect from the intermediate principal stress being neglected. MC can be written as a function of major and minor principal stresses, or normal stress and shear stress on the failure plane. The shape of the failure surface in principal stress space is dependent on the form of the failure criterion: linear functions map as planes and nonlinear functions as curvilinear surfaces. Mohr's criterion allows for a curved shape of the failure envelope, and this nonlinear behavior is exhibited by many rock types. The advantages of the MC failure criterion are its mathematical simplicity, clear physical meaning of the material parameters, and general level of acceptance.