  The "true muonium" (mu^+ mu-) and "true tauonium" (tau^+ tau^-) bound states
are not only the heaviest, but also the most compact pure QED systems. The
rapid weak decay of the tau makes the observation of true tauonium difficult.
However, as we show, the production and study of true muonium is possible at
modern electron-positron colliders.
