  The parsec-scale radio properties of blazars detected by the Large Area
Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been
investigated using observations with the Very Long Baseline Array (VLBA).
Comparisons between LAT and non-LAT detected samples were made using
contemporaneous data. In total, 232 sources were used in the LAT-detected
sample. This very large, radio flux-limited sample of active galactic nuclei
(AGN) provides insights into the mechanism that produces strong gamma-ray
emission. It has been found that LAT-detected BL Lac objects are very similar
to the non-LAT BL Lac objects in most properties, although LAT BL Lac objects
may have longer jets. The LAT flat spectrum radio quasars (FSRQs) are
significantly different from non-LAT FSRQs and are likely extreme members of
the FSRQ population. Contemporaneous observations showed a strong correlation,
whereas no correlation is found using archival radio data. Most of the
differences between the LAT and non-LAT populations are related to the cores of
the sources, indicating that the gamma-ray emission may originate near the base
of the jets (i.e., within a few pc of the central engine). There is some
indication that LAT-detected sources may have larger jet opening angles than
the non-LAT sources. Strong core polarization is significantly more common
among the LAT sources, suggesting that gamma-ray emission is related to strong,
uniform magnetic fields at the base of the jets of the blazars. Observations of
sources in two epochs indicate that core fractional polarization was higher
when the objects were detected by the LAT. Included in our sample are several
non-blazar AGN such as 3C84, M82, and NGC 6251.
