  Perturbative QCD has made significant progress over the last few decades. In
the first part, we present an introductory overview of perturbative QCD as seen
from a modern viewpoint. We explain the relation between purely perturbative
predictions and predictions based on Wilsonian effective field theories. We
also review progress of modern computational technologies and discuss
intersection with frontiers of mathematics. Analyses of singularities in
Feynman diagrams play key roles towards developing a unified view. In the
second part, we discuss application of perturbative QCD, based on the
formulation given in the first part, to heavy quarkonium systems and the
interquark force between static color charges. We elucidate impacts on order
Lambda_QCD physics in the quark mass and interquark force, which used to be
considered inaccessible by perturbative QCD.
