Supermassive Black Holes grow at the center of galaxies in consonance with them .
In this review we discuss the mass feeding mechanisms that lead to this growth in Active Galactic Nuclei ( AGN ) , focusing on constraints derived from observations of their environment , from extragalactic down to galactic and nuclear scales .
At high AGN luminosities , galaxy mergers and interactions play an important role in AGN triggering and feeding .
However , gas chaotic cold accretion in galaxy clusters can trigger radiatively inefficient AGNs in brightest cluster galaxies ( BCGs ) .
At lower luminosities , minor mergers feed AGN in early-type , gas-starving galaxies , while secular processes dominate in later-type , gas-rich galaxies .
While bars do not appear to directly feed AGNs , AGN flickering leads to the dissociation between small and large scales , hence affecting the interpretation of cause and effect .
At \sim 100 pc scales , recent observations have revealed compact disks and inflows along nuclear gaseous spirals and bars , while chaotic cold accretion continues to feed BCGs at these scales .
Estimated mass inflow rates – of 0.01 to a few M _ { \odot } yr ^ { -1 } – are in many cases a thousand times higher than the mass accretion rate to the supermassive black hole .
As a result , 10 ^ { 6 } –10 ^ { 9 } M _ { \odot } gas reservoirs can be built on 10 ^ { 7 - 8 } yr , that in turn may lead to the formation of new stars and/or be ejected via the onset of AGN feedback .