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An accretion flow onto a supermassive black hole is the primary processpowering quasars. However, a geometry of this flow is not well constrained.Both global MHD simulations and observations suggest that there are severalemission components present in the nucleus: an accretion disk, hot plasma(corona or sphere) with electrons scattering the optical and UV photons, and anoutflow (wind/jet). The relative location and size of these emissioncomponents, as well as their "interplay" affect the emerging quasar spectrum. Ireview briefly standard accretion disk models and the recent progress, pointout discrepancies between the predicted and observed spectra and discuss someissues in fitting these models to the broad-band spectral energy distributionof quasars. I present examples of models fitted simultaneously to theoptical-UV-X-ray data and possible constraints on the parameters.

Models of Accretion Disks