  We discuss the recent status in the theoretical understanding of dilepton
production in central heavy-ion reactions with the Pb-beam at the full CERN-SpS
energy of 158 AGeV. In the low-mass region ($M\le$~1 GeV) a strong broadening
of the vector meson resonances in hot and dense matter (especially for the
$\rho$ meson) entails thermal dilepton rates very reminiscent to perturbative
$q\bar q$ annihilation close to the expected phase boundary of the chiral
symmetry restoring transition. A consistent description of the experimentally
observed enhancement at both low and intermediate masses (1.5 GeV~$\le M \le$~3
GeV) in terms of thermal radiation from an expanding fireball can be obtained.
