  At the dawn of a new theoretical tool based on the AdS/CFT correspondence for
nonperturbative aspects of quantum chromodynamics, we give an interim review on
the new tool, holographic QCD, with some of its accomplishment. We try to give
an A-to-Z picture of the holographic QCD, from string theory to a few selected
top-down holographic QCD models with one or two physical applications in each
model. We may not attempt to collect diverse results from various holographic
QCD model studies.
