  We discuss the problem of the formation of a large-scale magnetic field in
the accretion disks around black holes, taking into account the non-uniform
vertical structure of the disk. The high electrical conductivity of the outer
layers of the disk prevents the outward diffusion of the magnetic field. This
implies a stationary state with a strong magnetic field in the inner parts of
the accretion disk close to the black hole, and zero radial velocity at the
surface of the disk. Structure of advective accretion disks is investigated,
and conditions for formation of optically thin regions in central parts of the
accretion disk are found. The problem of jet collimation by magneto-torsion
oscillations is considered.
