Abstract <p>The basic properties of Be stars and X-ray binary systems containing these stars are considered. In the vast majority of these systems the Be stars’ companions are neutron stars accreting matter from the decretion disk of a rapidly rotating Be star. The observed properties of such systems are studied within the framework of the hypothesis that the reason for the high rotational velocity of Be stars is the large initial angular momentum of the protostellar cloud, and during the evolution of the star on the main sequence, the angular momentum is transferred from the interior of the star to the surface. The work uses the results of calculations performed earlier by the authors of the evolution of rapidly rotating Be stars, taking into account their stellar wind, which carries away the angular momentum of the outer layers of the star. Based on the rates of rotational mass loss by Be stars through the decretion disk, obtained in these calculations, it is estimated which part of the disk material is captured by the neutron star in observed X-ray binaries with Be stars. For systems with short orbital periods of about 30 days, the maximum value of this part can exceed 0.01. At the same time, for observed systems, this part significantly (sometimes by more than 2 orders of magnitude) exceeds the fraction of the Be star’s stellar wind captured by the neutron star.</p>