After reviewing the X-ray evidence of massive, high-velocity outflows in nearby and distant AGNs/QSOs, I will discuss their relevance for understanding the formation of AGN winds, as well as estimating the amount of mechanical feedback released by AGNs into their host galaxies. I will show some analogies, as well as differences, between AGN winds and outflows found in galactic BH/NS binaries, and will briefly list some of the future advancements in this field to be expected from existing (XMM, Chandra, Suzaku, Nustar), near-future (Astro-H) and future (Athena) high-energy observatories.