  We present first-epoch, milliarcsecond-scale linear polarization images at 15
GHz of 133 jets associated with AGN in the MOJAVE survey (Monitoring of Jets in
Active Galactic Nuclei with VLBA Experiments). The sample consists of all known
AGN with galactic latitude |b| > 2.5 deg., J2000 declination > -20 deg., and 15
GHz VLBA flux density exceeding 1.5 Jy (2 Jy for sources with declination < 0)
at any epoch during the period 1994-2003. Because of strong selection effects,
the sample primarily consists of blazars with parsec-scale morphologies
consisting of a bright core component at the extreme end of a one-sided jet. At
least one third of the compact cores are completely unresolved on the longest
VLBA baselines, indicating brightness temperatures above 10^{11} K. The
unresolved cores tend to have electric vectors that are aligned with the inner
jet direction, suggesting the presence of a stationary transverse shock near
the base of the jet. Many of the extended jet regions display exceedingly high
fractional polarizations (> 50%) and electric vectors aligned with the jet
ridge line, consistent with optically thin emission from transverse shocks.
Both weak- and strong-lined blazars show a general increase in fractional
polarization with distance down the jet, but BL Lac jets are generally more
polarized and have electric vectors preferentially aligned with the local jet
direction. We show that these differences are intrinsic to the jets, and not
due to sample bias. Distinct features in the jets of gamma-ray loud (EGRET)
blazars are typically twice as luminous as those in non-EGRET blazars, and are
more polarized. These differences can be adequately explained if EGRET blazars
have slightly higher Doppler boosting factors than those not yet detected in
gamma-rays.
