  A review of wind accretion in high-mass X-ray binaries is presented. We focus
attention to different regimes of quasi-spherical accretion onto the neutron
star: the supersonic (Bondi) accretion, which takes place when the captured
matter cools down rapidly and falls supersonically toward NS magnetospghere,
and subsonic (settling) accretion which occurs when plasma remains hot until it
meets the magnetospheric boundary. Two regimes of accretion are separated by an
X-ray luminosity of about $4\times10^{36}$ erg/s. In the subsonic case, which
sets in at low luminosities, a hot quasi-spherical shell must be formed around
the magnetosphere, and the actual accretion rate onto NS is determined by
ability of the plasma to enter the magnetosphere due to Rayleigh-Taylor
instability. We calculate the rate of plasma entry the magnetopshere and the
angular momentum transfer in the shell due to turbulent viscosity appearing in
the convective differentially rotating shell. We also discuss and calculate the
structure of the magnetospheric boundary layer where the angular momentum
between the rotating magnetosphere and the base of the differentially rotating
quasi-spherical shell takes place. We show how observations of equilibrium
X-ray pulsars Vela X-1 and GX 301-2 can be used to estimate dimensionless
parameters of the subsonic settling accretion theory, and obtain the width of
the magnetospheric boundary layer for these pulsars.
