Weak decays of open and hidden top

Within the present standard model of electroweak interaction it is most natural to expect top: a sixth quark which - together with the well established b - completes the third weak isodoublet of quarks. Experimentally no signal for toponium has been found up to 37 GeV. The author treats in some detail electroweak annihilation decays. He then comments on parity mixing in toponium. Single quark decays as means to determine t-quark lifetimes are discussed and decay properties of top mesons are studied. Finally future prospects of ultrahigh energies using linear colliders are considered and some predictions for decays of superheavy quarks are given. (Auth.)