  The goal of these lectures, oriented towards the students just entering the
field, is to provide an elementary introduction to QCD and the physics of
nuclear interactions at high energies. We first introduce the general structure
of QCD and discuss its main properties. Then we proceed to Glauber multiple
scattering theory which lays the foundation for the theoretical treatment of
nuclear interactions at high energies. We introduce the concept of Gribov's
inelastic shadowing, crucial for the understanding of quantum formation
effects. We outline the problems facing Glauber approach at high energies, and
discuss how asymptotic freedom of QCD helps to resolve them, introducing the
concepts of parton saturation and color glass condensate.
