Mass outflows from accretion disks: Old and new challenges

We summarize recent developments in modeling of mass outflows from accretion disks in AGN. We illustrate how the hydrodynamical and magnetohydrodynamical wind structures revealed in numerical simulations relate to observations. Important results from the numerical simulations include: no shielding from X-rays is needed to radiatively launch a wind from the inner disk; shielding is needed to accelerate the wind to high velocities. Disk winds launched magnetically seem to be too dense to be accelerated by line driving. It appears that we have an all or nothing situation for radiation-driving: radiation driving has to be responsible for both launching and accelerating the wind or a wind launched by some other mechanism must have a very finely tuned density in order to be accelerated by radiation driving to velocities as high as measured in BAL QSOs.