We review the properties of energetic parton propagation in hot or cold QCD matter, as obtained in recent work. The medium induced energy loss is studied. It has the remarkable feature to grow as L², the length of the traversed matter squared. Numerical estimates suggest that it may be significantly enhanced in hot matter compared to cold matter, thus pointing towards a possible signal for quark--gluon plasma formation. The more realistic case of an expanding (longitudinally) QCD plasma is studied. The resulting radiative energy loss can be as large as 6 times the corresponding one in a static plasma at the reference temperature T(L) which is reached after the parton propagates on a distance L. Finally, the spectrum of soft radiated gluons is studied, leading to the calculation of the medium dependent energy lost by a jet with opening angle \theta _cone. It is shown that the fraction of this energy loss to the integrated one exhibits a universal behavior in terms of \theta _cone² L³ \mathaccent "0362\relax {mathaccent "0362\relax {q} where \mathaccent "0362\relax {q} is the transport coefficient characterizing the medium. Phenomenological implications for the difference between hot and cold matter are discussed.

PACS numbers: 12.38.Bx, 12.38.Mh, 24.85.+p