The monograph is devoted to the presentation of methods for the study of macroscopic kinetics problems based on the geometric theory of singular perturbations. The mathematical apparatus described in the book is used for the development of the fundamental ideas of N. from the same positions. N. Semenova, related to the method of quasi-stationary concentrations and methods of the theory of thermal ignition and applied to the study of specific nonlinear problems of chemical kinetics, biophysics, laser physics The book does not require deep mathematical preparation - the necessary information is given mainly in the form of ready-made recipes. The book is intended for students, graduate students, teachers, researchers and engineers for whom problems of simplification of models, definition of critical modes and safety of reaction systems are of scientific or industrial interest.