  Medium modifications of the electromagnetic spectral function in hadronic and
quark-gluon matter are reviewed. A strong broadening of the $\rho$ meson, which
dominates the spectral function in the low-mass regime, is quantitatively
consistent with dilepton excess spectra measured in photoproduction off cold
nuclei (CLAS/JLab) and in fixed-target ultrarelativistic heavy-ion collisions
(NA45,NA60/CERN-SPS). The large excess observed by PHENIX at RHIC remains
unexplained to date, but is most likely not due to emission from the
Quark-Gluon Plasma. Connections to thermal lattice QCD promise progress in the
search for chiral symmetry restoration.
