Review of $e^{+}{e}^{-}$ physics at PETRA

A review is given of the experimental investigation of high-energy $e^{+}{e}^{-}$ interactions at PETRA, the electronpositron colliding beam accelerator at DESY in Hamburg, Germany. The energy of the machine is such that the strong, electromagnetic, and weak interactions start to play a role in the processes which can be studied. Results are presented on tests of quantum electrodynamics studying $e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, and ${\tau }^{+}{\tau }^{-}$. The fermion pair production processes $e^{+}{e}^{-}\to F\overline{F}$, where the $F\overline{F}$ pair stands for either a lepton pair ($e^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{-}$, and ${\tau }^{+}{\tau }^{-}$) or a quark-antiquark pair, are investigated to study the effects of the $Z^{\circ }$ exchange. The measurements of $R$, the ratio of hadronic to pointlike muon pair cross section, the search for new quark flavors, and other new particles are reviewed. Finally the discovery of three-jet events arising from the radiation of hard noncollinear gluons as predicted by quantum chromodynamics and the determinations of the strong coupling constant ${\alpha }_s$ are discussed.