The book is devoted to the solution of one general problem of the theory of a three-dimensional quasi-stationary sinusoidal and pulse electromagnetic field. These studies, unlike many well-known works, are based on obtained exact analytical solution of the problem for the field, generated by external current sources near the conducting body with plane surface. The solution for the vector and scalar potentials, electric and magnetic intensities in the dielectric and conducting media is found without restrictions on the configuration of current sources, properties of the media and field frequency. Some general properties of field formation for arbitrary field in the considered system are obtained (in particular, full compensation by the field of the electric charge distributed on the interface between the media, the normal component of the induced external electric field and, accordingly, the equality to zero the components both of the current density and the electric field intensity perpendicular to the interface; the non-uniform electromagnetic field decreases in depth of conducting medium faster than uniform field). It is shown that the exact analytical solution depends on the values of the parameter proportional to the ratio of the field penetration depth to the distance between the external field sources and the body. The concept of strong skin effect is extended to the case of small value of the introduced parameter. A significant simplification of the expressions was obtained as an asymptotic expansion on this small parameter. In the case of pulsed fields approximate method gives the highest accuracy during important initial period of pulse time. For asymptotic expansion the approximate impedance boundary condition is generalized to the diffusion of non-uniform field into conducting medium. The book is intended for the researchers, postgraduate students and students specialized in theory and calculations of electromagnetic fields.