In Chapter 4, firstly a few basic terms (object and configuration, stress, strain, and constitutive relation between stress tensor and strain tensor), three coordinate systems (shape coordinate, lattice coordinate, and laboratory coordinate), deformation gradient as well as fundamental equations in continuum mechanics are briefly recalled for the sake of understanding fundamental equations of the crystal plasticity finite element method (CPFEM). A few advantages of CPFEM (including its abilities to analyze multiparticle problems and solve crystal mechanics problems with complex boundary conditions) are highlighted. Then, representative mechanical constitutive laws of crystal plasticity including dislocation-based constitutive models and constitutive models for displacive transformation are briefly described, followed by a short introduction to the finite element method (FEM), several FEM software packages (including Adina, ABAQUS, Deform, and ANSYS) and a procedure for CPFEM simulation. Finally, a case study of plastic deformation-induced surface roughening in Al polycrystals is demonstrated to show important features of crystal plasticity finite element method in materials design.