  We review weakly-bound heavy quarkonium systems using effective field
theories of QCD. We concentrate on potential Non-Relativistic QCD, which
provides with a well founded connection between QCD and descriptions of the
heavy quarkonium dynamics in terms of Schr\"odinger-like equations. This
connection is obtained using standard quantum field theory techniques such as
dimensional regularization, which is used throughout, and renormalization.
Renormalization group equations naturally follow. Certain effort is made to
illustrate how computations are performed and the necessary techniques,
providing some examples. Finally, we briefly review a selected set of
applications, which include spectroscopy, radiative transitions,
Non-Relativistic sum rules, inclusive decays, and electromagnetic threshold
production.
