Classical chromo-dynamics of relativistic heavy ion collisions

Relativistic heavy ion collisions produce thousands of particles, and it is sometimes difficult to believe that these processes allow for a theoretical description directly in terms of the underlying theory - QCD. However once the parton densities are sufficiently large, an essential simplification occurs - the dynamics becomes semi-classical. As a result, a simple ab initio approach to the nucleus--nucleus collision dynamics may be justified. In these lectures, we describe the application of these ideas to the description of multi--particle production in relativistic heavy ion collisions. We also discuss the role of semi-classical fields in the QCD vacuum in hadron interactions at low and high energies.