In the book of the famous popularizer of science A. Asimov in a lively and popular form presents modern ideas about the most elusive particle of the microcosm - neutrinos Asimov traces the chain of events that led physicists to the discovery of neutrinos, tells about how this particle has learned to register, about its role in the evolution of the Universe, about the latest achievements of neutrino physics - the two-neutrino experiment. The author seeks to reveal to the reader a modern physical picture of the world, but at the same time not to suppress it with a mass of information so extensive in this field of science. The book will be of interest to the widest range of readers: schoolchildren, teachers and those who follow the latest achievements of physics.