In recent decades electronics devices are widely used and due to influence of direct and indirect lightning on normal function of these devices, protection of them against lightning is important. Lightning is a phenomenon which has effect on power quality and system reliability of the power distribution systems. Due to height and location of the power distribution lines indirect lighting stroke has more influence on distribution system with respect to direct stroke. Chapter one shortly deals with physics of lightning and lightning protection of power system. In this chapter at frist we discuss about physics of lightning and different types of linghtning, then computation of lightning stroke to overhead transmission lines are dicussed.