This book is an introduction to the calculus of variations, aimed at minimizing or maximizing real-valued functionals. The functionals are integrals over an interval, which is why the permissible functions depend on only one independent variable. The questions are motivated by many examples, some of which are historically significant. The theory introduces the Euler-Lagrange calculus and the direct methods of the calculus of variations. The explanations are accompanied by illustrations that facilitate understanding. Each section includes exercises, with solutions provided at the end of the book. The book is suitable for a lecture in the bachelor's program starting from the 3rd semester. The supplementary materials that go beyond the basic lectures are provided in the text or in the appendix.