  The most luminous quasars (with bolometric luminosities are 1E47 erg/s) show
a high prevalence of CIV {\lambda}1549 and [OIII]{\lambda}{\lambda}4959,5007
emission line profiles with strong blueshifts. Blueshifts are interpreted as
due to Doppler effect and selective obscuration, and indicate outflows
occurring over a wide range of spatial scales. We found evidence in favor of
the nuclear origin of the outflows diagnosed by [OIII]{\lambda}{\lambda}
4959,5007. The ionized gas mass, kinetic power, and mechanical thrust are
extremely high, and suggest widespread feedback effects on the host galaxies of
very luminous quasars, at cosmic epochs between 2 and 6 Gyr from the Big Bang.
In this mini-review we summarize results obtained by our group and reported in
several major papers in the last few years with an eye on challenging aspects
of quantifying feedback effects in large samples of quasars.
