The theory of an electromagnetic field is a concluding subject in the curriculum of the theoretical training of electrical engineers. The field theory course usually follows the course in the basic theory of electric circuits.The author covers the basic aspects of the theory of an electromagnetic field within the restricted space so that the text can fit the interest of students and answer the practical engineering needs. The emphasis therefore is on the behavior of fer­ romagnetic bodies in an electromagnetic field and on the processes in real imperfect dielectrics and poor conductors. The text also gives strict definitions of the basic vec­ tors and shows the differences between them.Many of the aspects discussed in the book focus on the problems one has to deal with in electrical engineering practice. This is one of the factors that influenced the organization of the book and the manner of presentation of the material. A similar treatment of the field theory was also given in the book by A. Netushil and K. Polivanov The Theory o f Electromagnetic Field. Theoretical Principles o f Elec­ trical Engineering. Part 3 (Gosenergoizdat, in Russian). No effort has been made to cite a great number of contributors in this area. In the author's opinion, of many valuable texts, the following books will be very helpful to students in the study of the theory of electrical engineering: Analysis and Synthesis o f Electric Circuits (Mir Publishers) by G. Zeveke, P. Ionkin, A. Netushil, and S. Strakhov, The Feynman Lectures on Physics (Addison-Wesley) by R. Feynman, R. Leighton, and M. Sands, Electricity and Magnetism (McGraw-Hill) by E. Purcell that treats the effects of moving bodies in an electromagnetic Field, and Fundamentals o f the Theory o f Elec­ tricity (Mir Publishers) by I. Tamm. Special mention should be made of Maxwell's Treatise on Electricity and Magnetism which forms the basis of the course in the field theory.In preparing the book for its publication in English, the author revised the text and added some useful information.