  We study the composition of the faint radio population selected from the
VLA-COSMOS 3GHz Large Project, a radio continuum survey performed at 10 cm
wavelength. The survey covers the full 2 square degree COSMOS field with mean
$rms\sim2.3$ $\mu$Jy/beam, cataloging 10,899 source components above $5\times
rms$. By combining these radio data with UltraVISTA, optical, near-infrared,
and Spitzer/IRAC mid-infrared data, as well as X-ray data from the Chandra
Legacy, and Chandra COSMOS surveys, we gain insight into the emission
mechanisms within our radio sources out to redshifts of $z\sim5$. From these
emission characteristics we classify our souces as star forming galaxies or
AGN. Using their multi-wavelength properties we further separate the AGN into
sub-samples dominated by radiatively efficient and inefficient AGN, often
referred to as high- and low-excitation emission line AGN. We compare our
method with other results based on fitting of the sources' spectral energy
distributions using both galaxy and AGN spectral models, and those based on the
infrared-radio correlation. We study the fractional contributions of these
sub-populations down to radio flux levels of $\sim$10 $\mu$Jy. We find that at
3 GHz flux densities above $\sim$400 $\mu$Jy quiescent, red galaxies,
consistent with the low-excitation radio AGN class constitute the dominant
fraction. Below densities of $\sim$200 $\mu$Jy star-forming galaxies begin to
constitute the largest fraction, followed by the low-excitation, and X-ray- and
IR-identified high-excitation radio AGN.
