Energy and virtuality scale dependence in quark and gluon jets

We discuss some important issues concerning multiplicities in quark and glu on jets in e(+)e(-) annihilation. In QCD the properties of a jet in general depends on two scales, the energy and virtuality of the jet. Frequently th eoretical predictions apply to a situation where these scales coincide, whi le for experimental data they are often different. Thus an analysis to extr act e.g. the asymptotic multiplicity ratio C-F/C-A between quark and gluon jets, needs a carefully specified jet definition, together with a calculati on of nonleading corrections to the multiplicity evolution. We propose meth ods to systematically study the separate dependence upon the two scales in experimental data and compare the results with theory. We present jet findi ng algorithms which correspond well to the theoretically considered jets. W e also show that recoil effects add corrections to the modified leading log approximation which are quantitatively important, though formally suppress ed at high energies.