  We present a review of parton saturation/Color Glass Condensate physics in
the context of deuteron-gold ($d+Au$) collisions at RHIC. Color Glass
Condensate physics is a universal description of all high energy hadronic and
nuclear interactions. It comprises classical (McLerran-Venugopalan model and
Glauber-Mueller rescatterings) and quantum evolution (JIMWLK and BK equations)
effects both in small-$x$ hadronic and nuclear wave functions and in the high
energy scattering processes. Proton-nucleus (or $d+A$) collisions present a
unique opportunity to study Color Glass Condensate predictions, since many
relevant observables in proton-nucleus collisions are reasonably
well-understood theoretically in the Color Glass Condensate approach. In this
article we review the basics of saturation/Color Glass Condensate physics and
reproduce derivations of many important observables in proton
(deuteron)--nucleus collisions. We compare the predictions of Color Glass
physics to the data generated by $d+Au$ experiments at RHIC and observe an
agreement between the data and the theory, indicating that Color Glass
Condensate has probably been discovered at RHIC. We point out further
experimental measurements which need to be carried out to test the discovery.
