Quarkonia and their transitions

Valuable data on quarkonia (the bound states of a heavy quark Q=c,b and the corresponding antiquark) have recently been provided by a variety of sources, mainly e+ e- collisions, but also hadronic interactions. This permits a thorough updating of the experimental and theoretical status of electromagnetic and strong transitions in quarkonia. We discuss QQbar transitions to other QQbar states, with some reference to processes involving QQbar annihilation.