  Where do quasars reside? Are quasars located in environments similar to those
of typical L* galaxies, and, if not, how do they differ? An answer to this
question will help shed light on the triggering process of quasar activity. We
use the Sloan Digital Sky Survey to study the environment of quasars and
compare it directly with the environment of galaxies. We find that quasars (M_i
< -22, z < 0.4) are located in higher local overdensity regions than are
typical L* galaxies. The enhanced environment around quasars is a local
phenomenon; the overdensity relative to that around L* galaxies is strongest
within 100 kpc of the quasars. In this region, the overdensity is a factor of
1.4 larger than around L* galaxies. The overdensity declines monotonically with
scale to nearly unity at ~1 Mpc, where quasars inhabit environments comparable
to those of L* galaxies. The small-scale density enhancement depends on quasar
luminosity, but only at the brightest end: the most luminous quasars reside in
higher local overdensity regions than do fainter quasars. The mean overdensity
around the brightest quasars (M_i < -23.3) is nearly three times larger than
around L* galaxies while the density around dimmer quasars (M_i = -22.0 to
-23.3) is ~1.4 times that of L* galaxies. By ~0.5 Mpc, the dependence on quasar
luminosity is no longer significant. The overdensity on all scales is
independent of redshift to z = 0.4. The results suggest a picture in which
quasars typically reside in L* galaxies, but have a local excess of neighbors
within ~0.1 - 0.5 Mpc; this local density excess likely contributes to the
triggering of quasar activity through mergers and other interactions.
