  We discuss systems containing a heavy quark and a heavy antiquark in the
infinite mass limit of QCD. Studying the limit of equal velocities for both
heavy particles, we formulate an effective theory approach to heavy
quarkonia-like systems. The method is well suited to processes in which the two
heavy quarks annihilate, such as electromagnetic and strong decays of
charmonium and bottomonium and weak decays of $B_c$.
