The book is devoted to methods for calculating electric and magnetic fields in various electrophysical devices. It contains a description of mathematical statements and algorithms for problems of electro- and magnetostatics, the formation of dense beams of charged particles, microwave electronics. For various types of problems, methods of finite differences, finite elements and integral equations are used. Examples of solving typical problems are given. The issues of automation of calculations of a wide class of devices and technology of application packages are considered. For specialists in applied mathematics and engineers.