  In this Chapter QCD interactions between a quark and an anti-quark are
discussed. In the heavy quark limit these potentials can be related to
quarkonia and $1/m$ corrections can be systematically determined. Excitations
of the ground state potential provide an entry point into the phenomenology of
quark-gluon hybrids. The short-distance behaviour of non-perturbative
potentials can serve as a test of resummation and convergence of perturbative
expansions. Torelons and potentials between non-fundamental colour charges
offer a window into the origin of the confinement mechanism and relate to
effective string descriptions of low energy aspects of QCD.
