In Ansys Polyflow, the Darcy model is used to calculate flows involving porous media, such as the flow of oil in sand, or of a polymer through a mat. Sub-tasks of the Darcy type are available in 2D and 3D, in steady-state and time-dependent modes. Although multi-material simulations can be performed by defining several sub-tasks, the description in this chapter is limited to a single sub-task, since the procedure follows the general principle of assembling several sub-tasks in a single task.