The complex physics of multiphase flow in porous media are usually modeled at the field scale using Darcy-type formulations. The key descriptors of such models are the relative permeabilities to each of the flowing phases. It is well documented that, whenever the fluid saturations undergo a cyclic process, relative permeabilities display hysteresis effects. The main mechanism for hysteresis is trapping of the non- wetting phase during an imbibition process (increasing wetting-phase saturations). Different multiphase relative permeability, trapping and hysteresis models are reviewed in this book. Then the way by which hysteresis in relative permeability can be applied in simulation of cyclic processes in different commercial reservoir simulators, is indicated.