Great progress has been made in developing and using numerical methods for solving electromagnetic field problems at low frequency recently. Many of these problems refer to eddy currents which appear in various electromagnetic devices. Originally such problems were tackled by analytical solutions which are limited to simple geometries and linear materials. In practice though all electromagnetic devices have complex boundaries, include non-linear materials, and may be treated exclusively by numerical methods. This book gives systematically the matehmatical simulation of existing methods and discusses the siscretization of relevant equations. The methods described are: finite difference, finite sums, finite element, boundary element, and some variants. Physical connotations of methods and problems are also given.