Heavy Quarkonia

We review a decade of studies devoted to the physics of heavy quark bound states $cc$ and $bb$. After addressing the question of why, how and where to perform these investigations, we turn to an analysis of the spin (in-)dependent forces acting between heavy quarks. Processes involving large momentum transfer allow a determination of the coupling constant of the strong interaction. A critical evaluation is given on the possibility to accurately determine the strong coupling. For a description of hadronic transitions within heavy quarkonia non-perturbative methods have been developed. Except for one possible problem, these calculations will be shown to be in good agreement with data. Heavy quarkonia decays to light mesons provide the means to investigate known low mass states and to search for new forms of matter. Finally, an evaluation is attempted of the physics prospects which are achievable with significantly larger data sets than those available today