  HST observations of eight intrinsically luminous quasars with redshifts
between $0.16$ and~$0.29$ are presented. Seven companion galaxies brighter than
$M_V = -16.5$ lie within a projected distance of 25 kpc of the quasars; three
of the companions are located closer than $3''$ (6 kpc projected distance) from
the quasars, well within the volume that would be enclosed by a typical $L^*$
host galaxy. The observed association of quasars and companion galaxies is
statistically significant and may be an important element in the
luminous-quasar phenomenon. Evidence for candidate host galaxies is presented
for the three most promising cases: PG 1116+215, 3C 273, and PG 1444+407, but
additional observations are required before the characteristics of the
candidate hosts can be regarded as established. Upper limits are placed on the
visual-band brightnesses of representative galactic hosts for all of the
quasars. These limits are established by placing galaxy images obtained with
HST underneath the quasars and measuring at what faintness level the known
galaxies are detected. On average, the HST spirals would have been detected if
they were one magnitude fainter than $L^*$ or brighter and the early-type
galaxies could have been detected down to a brightness level of about $L^*$,
where $L^*$ is the Schechter characteristic luminosity of field galaxies.
