The role of twinning in the anisotropic behavior and ductility of magnesium alloys is analyzed at ambient as well as elevated temperatures. Magnesium alloy AZ31B sheet is investigated as a model system, because it is the most common wrought magnesium alloy. Uniaxial compression tests are conducted at room temperature and at elevated temperatures to measure the anisotropy of the strength and strain at various strain levels.A viscoplastic self-consistent polycrystal modeling approach was used to model the deformation behavior; including the anisotropy and texture evolution. Temperature dependence of parameters affecting activity of different deformation modes, such as Critical Resolved Shear Stress (CRSS) and strain hardening, and the volume fraction of twinned grains are investigated with the help of the polycrystal plasticity model.The model, thus developed, could find application for predicting material's response in complex loading conditions.