  The host galaxies of six nearby QSOs are studied on the basis of high
resolution HST optical images and spatially resolved VLT slit spectra. The gas
ionization and velocity are mapped as a function of the distance to the central
QSO. In the majority of the cases, the QSO significantly contributes to the gas
ionization in its whole host galaxy, and sometimes even outside.
  Reflection or scattering of the QSO \ha line from remote regions of the
galaxy is detected in several instances. The line shifts show that, in all
cases, the matter responsible for the light reflection moves away from the QSO,
likely accelerated by its radiation pressure.
  The two faintest QSOs reside in spirals, with some signs of a past
gravitational perturbation. One of the intermediate luminosity QSOs resides in
a massive elliptical containing gas ionized (and probably pushed away) by the
QSO radiation. The other medium-power object is found in a spiral galaxy
displaying complex velocity structure, with the central QSO moving with respect
to the bulge, probably as a result of a galactic collision. The two most
powerful objects are involved in violent gravitational interactions and one of
them has no detected host.
  These results suggest that (1) large-scale phenomena, such as galactic
collisions, are closely related to the triggering and the feeding of the QSO
and (2) once ignited, the QSO has significant influence on its large-scale
neighborhood (often the whole host and sometimes further away).
