The solution of many important problems of mathematical physics and technology cannot be expressed with the help of ordinary, elementary functions, and then special functions come to the aid (Legendary functions, Bessel functions, hypergeometric function, etc.) d. ). The theory of special functions is very detailed and includes an enormous number of formulas and ratios derived by a wide variety of methods, which makes it difficult to study it. The purpose of this book is to present the theory of special functions from a single point of view with the help of the theory of representations of groups. This approach allows to obtain in a single way all sorts of relationships between special functions, both previously known and new.