  Active galactic nuclei (AGN) are accreting supermassive black holes
co-evolving with their host galaxies through a complex interplay of feeding and
feedback. In this chapter, we first discuss AGN fuelling in galaxies, both in
interacting and isolated systems, focusing on the role that instabilities have
on the angular momentum budget of the gas. We then review observations and
models of feedback through AGN-driven winds from nuclear, sub-pc scales out to
galactic and circumgalactic medium scales. We continue with an overview of
surveys and statistical properties of the AGN population, before concluding
with a discussion on the prospects for the future facilities, focusing in
particular on Athena.
