When compiling this book, the authors had in mind to outline the basic information on the theory of complex numbers, more or less directly related to elementary mathematics. The book includes primarily four actions with complex numbers and extraction of roots from them. To this it was natural to add the basic theorem of algebra and a number of elementary consequences from it, essential in the theory of whole national functions and the theory of algebraic equations. Further applications showing the fruitfulness of introducing complex numbers into science include the Euler formula for imaginary indicators. It brings unity and completeness to the theory of elementary functions.