Recent results from PETRA on jet formation

In this talk I review data on the formation of hadronic jets obtained in e+e- collisions at the PETRA storage ring. The five large detectors CELLO, JADE, MARK J, PLUTO and TASSO have contributed to this subject. In the first part I concentrate on the evidence on QCD coming from the analyses of the e+e- annihilation into three (or more) hadronic jets. The combined results on energy flow, momentum flow, parton thrust, angular distributions as well as a comparison with other jet production models show that indeed the QCD model is at present the only one which gives a satisfactory description of all available data. In the second part I discuss the present status of the determination of the strong coupling constant αsub(s). The problem here arises from the inclusion of the next to leading order corrections, O(α2sub(s)), to the one-gluon bremsstrahlung cross sections: there are two different approaches leading to different values of αsub(s). Finally I present some results concerning the behaviour of quark and gluon jets; there are indications that quarks and gluons fragment differently: hadrons from a gluon-jet seem to have a larger mean transverse momentum (at a given jet energy) than the hadrons from a quark jet. (orig.)