The book is dedicated to the freely distributed Octave package. The reader holds in his hands the first description of the package in Russian. The built-in language of the package is described, and the graphical capabilities of the package are discussed in detail. The solution of various engineering and mathematical problems is considered in detail. Particular attention is paid to operations with matrices, solving nonlinear equations and systems, differentiation and integration, solving differential equations, optimization problems and processing of experimental data (interpolation and approximation). Along with the built-in language of the package, the QtOctave environment is described. The book is addressed to students, teachers of engineering and mathematics, as well as researchers.