  We review the basic concepts of perturbative quantum chromodynamics (QCD) and
relativistic hydrodynamics, and their applications to hadron production in high
energy nuclear collisions. We discuss results from the Relativistic Heavy Ion
Collider (RHIC) in light of these theoretical approaches. Perturbative QCD and
hydrodynamics together explain a large amount of experimental data gathered
during the first decade of RHIC running, although some questions remain open.
We focus primarily on practical aspects of the calculations, covering basic
topics like perturbation theory, initial state nuclear effects, jet quenching
models, ideal hydrodynamics, dissipative corrections, freeze-out and initial
conditions. We conclude by comparing key results from RHIC to calculations.
