  Different formalisms used in the perturbative approach to Thermal Field
Theory (TFT) are briefly reviewed. The rate of production of a virtual photon
in a quark-gluon plasma is then discussed to illustrate some features of TFT
before introducing the Hard Thermal Loop resummation which improves the
behaviour of the theory in the infrared sector. Some of the successes of this
appraoch are described before turning to the problems associated to the
undamped transverse gluon oscillations and the light-cone singularities arising
when on-shell and/or massless particles are involved.
