  Models of black hole accretion disks are reviewed, with an emphasis on the
theory of hard X-ray production. The following models are considered: i)
standard, ii) super-critical, iii) two-temperature, and iv) disk+corona. New
developments have recently been made in hydrodynamical models of accretion and
in phenomenological radiative models fitting the observed X-ray spectra.
Attempts to unify the two approaches are only partly successful.
