The permanent changes in shape and dimensions of metals can be carried out by plastic deformation mechanisms. Crystal structure and lattice parameters remain unaltered during plastic deformation. Plastic deformation increases the number of imperfections in metals. The two main processes involved in plastic deformation are slip and twinning. In slip, atoms move over a number of interatomic distances relative to their initial positions. The displacement step magnitude is equal to full interatomic distance. The orientation of displaced region and undeformed region remains the same. Movement by an atom is a fraction of interatomic distance in twinning process. The orientation of twinned region and untwined regions are not same. Slip mechanism is preferred during high temperature and lower strain rate cases. At lower temperature, high strain rate cases, twinning is employed.