  A review of wind accretion in HMXB is presented. We focus on different
regimes of quasi-spherical accretion onto a NS: supersonic (Bondi) accretion,
which takes place when the captured matter cools down rapidly and falls
supersonically towards the NS magnetosphere, and subsonic (settling) accretion
which occurs when the plasma remains hot until it meets the magnetospheric
boundary. The two regimes are separated by a limit in X-ray luminosity at about
4 10^{36} erg/s. In subsonic accretion, which works a hot quasi-spherical shell
must form around the magnetosphere, and the actual accretion rate onto the NS
is determined by the ability of the plasma to enter the magnetosphere due to
the Rayleigh-Taylor instability. Two regimes of subsonic accretion are
possible, depending on the plasma cooling mechanism (Compton or radiative) near
the magnetopshere. The transition from the high-luminosity regime with Compton
cooling to the low-luminosity (L_x < 3\times 10^35 erg/s) regime with radiative
cooling can be responsible for the onset of the 'off' states repeatedly
observed in several X-ray pulsars, such as Vela X-1, GX 301-2 and 4U 1907+09.
The triggering of the transition may be due to a switch in the X-ray beam
pattern in response to a change in the optical depth in the accretion column
with changing luminosity. We also show that in the settling accretion theory,
bright X-ray flares (10^{38}-10^{40} ergs) observed in SFXT may be produced by
sporadic capture of magnetized stellar-wind plasma. At sufficiently low
accretion rates, magnetic reconnection can enhance the magnetospheric plasma
entry rate, resulting in copious production of X-ray photons, strong Compton
cooling and ultimately in unstable accretion of the entire shell. A bright
flare develops on the free-fall time scale in the shell, and the typical energy
released in an SFXT bright flare corresponds to the mass of the shell.
