  The main characteristics of the average spectrum of radio quiet AGN in the UV
and X-ray range are reviewed, and the emission mechanisms are discussed in the
framework of accretion disk models, in particular the ``irradiated cold
relativistic disk". It is shown that some problems arise in confronting the
predictions of the model to the observations. We propose an alternative model
in terms of a hot disk surrounded by a cold Compton thick medium. Finally we
mention problems with remote regions of the accretion disk.
