  How does the gas get in nuclear regions to fuel black holes? How efficient is
the feedback? The different processes to cause rapid gas inflow (or outflow) in
galaxy centers are reviewed. Non axisymmetries can be created or maintained by
internal disk instabilities, or galaxy interactions. Simulations and
observations tell us that the fueling is a chaotic and intermittent process,
with different scenarios and time-scales, according to the various radial
scales across a galaxy.
