Quarks and gluons: tests of QCD in $e^{+}e^{-}$ annihilations

This article gives an overview of the main experimental tests of perturbative QCD performed at LEP. It covers the following topics: determination of alpha /sub s/ from event shapes, tests of flavour independence of alpha /sub s/, studies of heavy quark mass effects, differences between quark and gluon jet fragmentation and study of the triple gluon vertex. (56 refs).