The book acquaints the reader with complex numbers and functions of a complex argument (including Zhukovskyâs function as applied to the construction of a wing section). The material is presented in a geometric form. Complex numbers are considered as directed line segments and functions as mappings. To prepare the reader to such an understanding of complex numbers, we begin with a geometric interpretation of real numbers and operations on them. The book is based on a lecture delivered by the author to high-school students. To read the book, the reader need not be acquainted with complex numbers. It is intended for all those who are interested in mathematics and primarily for high-school students, it can also be of use for self-education. For proper comprehension of the content of the book the reader must posses high-school knowledge of mathematics.