  Heavy ion collisions pose interesting challenges to quantum chromodynamics,
because they probe the parton structure of the incoming nuclei at very small
longitudinal momentum fractions. Combined with the large size of nuclei, this
may lead to the phenomenon of gluon saturation. The Color Glass Condensate is
an effective QCD description that aims to cope with such a situation. In this
talk, I show how one may study heavy ion collisions in this framework.
