The existence of neutron stars was not only a brilliant theoretical prediction, but also one of the most unexpected and astonishing discoveries of all heavenly bodies. Twenty-five years after the remarkable event of their discovery, neutron stars, which are the densest, the most strongly magnetized, and the most rapid­ ly rotating bodies in the Galaxy, remain objects of intense interest. This book is a revised and enlarged version of the original Russian edition. The last five years were marked by the discovery of a supernova in the closest galaxy and dozens of X-ray sources and millisecond pulsars, which apparently confirm the validity of the basic ideas underlying these discoveries. The author has concentrated on the astrophysical manifestations of neutron stars, which are believed mainly to be associated with the nature of their interaction with their surroundings. Naturally, this approach does not leave much room for a detailed description of the internal structure of these stars. Fortunately, there exists an excellent monograph by S. L. Shapiro and S. A. Teukolsky (Black Holes, White Dwarfs, and Neutron Stars, Wiley, New York 1985) which deals mainly with the purely physical problems. Moreover, the publication of such a book in the West partly makes amends for the lack of information about the work being done by Soviet scientists in this field.