Static magnetic devices used in electromechanical energy conversion processes (e.g., rotating machines, rectifiers, inverters) are inductors and (permanent) magnets: their operation is based on Maxwell’s equations [1] and in particular for low-frequency (f < 50 kHz) applications on Ampere’s and Faraday’s laws neglecting displacement currents. Although the nonlinear characteristics of iron cores will be discussed in one of the following subsections, mostly ideal characteristics, that is, no iron-core losses (PFe = 0) and an infinitely large relative permeability (μr = ∞) will be assumed in this chapter. Computer-aided measurement techniques are introduced for measuring, as a function of frequency, small loss levels (few watts), impedances, resistances and inductances of inductors as used in solid-state energy conversion devices.