  We present the first catalog and data release of the Swift-BAT AGN
Spectroscopic Survey (BASS). We analyze optical spectra of the majority of AGN
(77%, 641/836) detected based on their 14-195 keV emission in the 70-month
Swift BAT all-sky catalog. This includes redshift determination, absorption and
emission line measurements, and black hole mass and accretion rate estimates
for the majority of obscured and un-obscured AGN (74%, 473/641) with 340
measured for the first time. With ~90% of sources at z<0.2, the survey
represents a significant census of hard-X-ray selected AGN in the local
universe. In this first catalog paper, we describe the spectroscopic
observations and datasets, and our initial spectral analysis. The FWHM of the
emission lines show broad agreement with the X-ray obscuration (~94%), such
that Sy 1-1.8 have NH<10^21.9 cm^-2, and Seyfert 2, have NH>10^21.9 cm^-2.
Seyfert 1.9 show a range of column densities. Compared to narrow line AGN in
the SDSS, the X-ray selected AGN have a larger fraction of dusty host galaxies
suggesting these types of AGN are missed in optical surveys. Using the most
sensitive [OIII]/Hbeta and [NII]/Halpha emission line diagnostic, about half of
the sources are classified as Seyferts, ~15% reside in dusty galaxies that lack
an Hbeta detection, but for which the line upper limits imply either a Seyfert
or LINER, ~15% are in galaxies with weak or no emission lines despite high
quality spectra, and a few percent each are LINERS, composite galaxies, HII
regions, or in known beamed AGN.
