Physics in Collision

The field of particle physics is developing very rapidly. During this past year, physicists added a new instrument to their arsenal for the study of quark-quark, quark-lepton, and lepton lepton interactions. This machine, the PROTON-ANTIPROTON COLLIDER, achieved the highest energy in the world. With its five detectors, it is beginning to explore hitherto inaccessible regions for new physics (Section I). Lepton-Iepto~ machines with detectors at full efficiency are producing copious data of the very highest precision. The possibility of glueballs and the detailing of the properties of the upsilon family have been of major importance this year (Section II). The particle jets which are believed to be direct manifesta tions of the quark structure of matter continue to provide valuable data against which we can test the ideas of QCD (Section III). With the advent of more and better data it is now possible to study in detail the formation evolution of hadronic states. Especially interesting are the properties of heavy quark states (Section IV). A far-seeing look into the future development of any fecund scienti fic field is rarely accurate, but is always stimulating (Section V). It is against this background of participating in the clarifi cation of the Physics in Collision that we continue this series.