An effective equivalent circuit method suitable for high-frequency usage is explained in this chapter. This equivalent circuit is based on the ladder network originally proposed by Wilhelm Cauer (1900–1945) in the field of network synthesis. This method enables a significant reduction in computations and also enables the coupled analysis of the magnetic field and the electric circuit. Models for the magnetic sheet and magnetic wire with a cylindrical shape are presented. Moreover, a universal method for the modeling of arbitrary eddy current fields is introduced.