The book is designed to teach the basics of object-oriented programming using the C # language and affects almost all major language tools, including namespaces, collection use, and network task programming. Particular attention is paid to the concepts of polymorphism and extensibility. The book is replete with numerous examples, which are functioning programs, and summary tables with a compact description of the main language tools. Aimed primarily at first-year students, the book is equally aimed at students at all levels for whom it will serve as an excellent guide, as well as anyone who works in other languages ​ ​ and wishes to switch to C #.