  Bound states of heavy $\bar{q}q$ quarks are reviewed within the context of
QCD. First of all, we consider the calculations which can be performed {\sl ab
initio}, which includes $\bar{t}t$ with principal quantum number $n$ up to
four,
  $\bar{b}b$ states with $n=1$ and (to a lesser extent)
  $\bar{b}b$ with $n=2$ and $\bar{c}c$ for $n=1$. Among the results, we report
a very precise $O(\alpha_s^4)$ evaluation of $b, c$ quark masses from
quarkonium spectrum with a potential to two loops, a calculation of the decay
$\Upsilon\to e^+e^-$ and a prediction for the splitting $\Upsilon - \eta_b$. We
then consider how, with the help of reasonable assumptions, one can extend QCD
calculations to other states of heavy quarks. Finally, a few words are said on
the treatment of light quark bound states.
