The book is a textbook on nonlinear oscillation theory and is an essential part of the . cycle. Unlike traditional vibration theory courses, the book is geared towards second-year students, which has defined a more popular style of presentation. The material of the book is carefully selected to serve as a sufficient basis for the formation of the reader, while avoiding cumbersome calculations and more special moments. The book consists of four main sections: , , Auto fluctuation & gt;, . A significant advantage of the course is the presence of a large number of tasks and exercises organically linked to the main presentation .. For students and graduate students of physical and physico-technical specialties of universities, as well as for researchers interested in the theory of oscillations and waves