  Accurate photometric redshifts are calculated for nearly 200,000 galaxies to
a 4.5 micron flux limit of ~13 uJy in the 8.5 deg^2 Spitzer/IRAC Shallow
survey. Using a hybrid photometric redshift algorithm incorporating both
neural-net and template-fitting techniques, calibrated with over 15,000
spectroscopic redshifts, a redshift accuracy of \sigma = 0.06(1+z) is achieved
for 95% of galaxies at 0<z<1.5. The accuracy is \sigma = 0.12(1+z) for 95% of
AGN at 0<z<3. Redshift probability functions, central to several ongoing
studies of the galaxy population, are computed for the full sample. We
demonstrate that these functions accurately represent the true redshift
probability density, allowing the calculation of valid confidence intervals for
all objects. These probability functions have already been used to successfully
identify a population of Spitzer-selected high redshift (z>1) galaxy clusters.
We present one such spectroscopically confirmed cluster at <z>=1.24, ISCS
J1434.5+3427. Finally, we present a measurement of the 4.5 micron-selected
galaxy redshift distribution.
