The book is an introduction to the theory of weak interaction of elementary particles. The first part contains detailed calculations of weak particle decays and reactions occurring under the influence of neutrinos. The second part outlines the basic ideas and equations of the electroweak interaction model and describes the properties of the vector bosons W± and Z0, discovered in 1983. The final chapters discuss the properties of hypothetical scalar bosons, the prospects for constructing a unified theory of all fundamental interactions, and the connection between particle physics and cosmology. Written on the basis of a course of lectures given by the author to students of the Moscow Institute of Physics and Technology. The first edition was published in 1981. For researchers, graduate students and students of physical specialties.