This thesis deals with the problem of a point source of harmonic current in a multilayer horizontally complex medium, where the first layer is air, while the other layers belong to a multilayer soil. Special attention is paid to the limiting case when in one of the soil layers the harmonic current source becomes a direct current source. The first chapter of the thesis is introductory and provides an introduction to the problem of a point source of transient current in a multilayer medium. The second chapter describes a multilayer horizontally complex model of the medium in which the transient potential distribution is calculated. Most of the transient electromagnetic models developed so far are limited to homogeneous soil, or to a two-layer medium (soil and air). Only in the last few years have transient electromagnetic models appeared that take into account multilayer soil. The third chapter presents Maxwell’s differential equations for an alternating harmonically varying electromagnetic field. For a quasi-static field distribution, the Helmholtz differential equation is reduced to the Poisson differential equation, and then the Poisson differential equation is solved and the potential retardation is subsequently introduced. The fourth chapter describes the limiting case when the current source becomes DC and describes the potential distribution for a point source of DC in a multilayer medium. The case in which the point source of DC is located in one of the layers of a multilayer soil is considered. A point source of DC in air cannot be realized if the usual assumption is made that the air conductivity is zero. The fifth chapter describes a point source of transient current in multilayer soil. When observing a point source of transient current in multilayer soil, from a practical point of view, the most interesting thing to observe is the lightning current. Here, the description of the transient current using the Heidler function, the mapping of the transient current from the time domain to the frequency domain and the calculation of the potential distribution using the IFFT algorithm are presented. The sixth chapter presents examples of calculating the potential distribution along a line and at a single point for different positions of a point source, i.e. for the case when the point source is located in the first, second and third soil layers.