Accretion Disk Models

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