  Photons and dileptons are being used to probe the properties of nuclear and
quark-gluon matter at high energy densities. This is an area where theory and
experiment are driving each other to obtain solid results. However, it is
important to clearly separate the assumptions and conclusions concerning the
correlation and response functions of a system in thermal equilibrium from the
space-time dynamics used to model the evolution of the matter created in the
nuclear collision.
