  CatWISE is a program to catalog sources selected from combined ${\it WISE}$
and ${\it NEOWISE}$ all-sky survey data at 3.4 and 4.6 $\mu$m (W1 and W2). The
CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data
collected from 2010 to 2016. This dataset represents four times as many
exposures and spans over ten times as large a time baseline as that used for
the AllWISE Catalog. CatWISE adapts AllWISE software to measure the sources in
coadded images created from six-month subsets of these data, each representing
one coverage of the inertial sky, or epoch. The catalog includes the measured
motion of sources in 8 epochs over the 6.5 year span of the data. From
comparison to ${\it Spitzer}$, the SNR=5 limits in magnitudes in the Vega
system are W1=17.67 and W2=16.47, compared to W1=16.96 and W2=16.02 for
AllWISE. From comparison to ${\it Gaia}$, CatWISE positions have typical
accuracies of 50 mas for stars at W1=10 mag and 275 mas for stars at W1=15.5
mag. Proper motions have typical accuracies of 10 mas yr$^{-1}$ and 30 mas
yr$^{-1}$ for stars with these brightnesses, an order of magnitude better than
from AllWISE. The catalog is available in the WISE/NEOWISE Enhanced and
Contributed Products area of the NASA/IPAC Infrared Science Archive.
