  We study e+e- pair production in proton-proton and in nucleus-nucleus
collisions from SIS to LHC energies within the parton-hadron-string dynamics
(PHSD) approach which incorporates explicit partonic degrees-of-freedom in
terms of strongly interacting quasiparticles (quarks and gluons) in line with
an equation-of-state from lattice QCD as well as the dynamical hadronization
and hadronic collision dynamics in the final reaction phase. We find a visible
in-medium effect in the low mass dilepton sector from dynamical vector-meson
spectral functions from SIS to SPS energies whereas at RHIC and LHC energies
such medium effects become more moderate. In the intermediate mass regime from
1.1 to 3 GeV pronounced traces of the partonic degrees of freedom are found at
SPS and RHIC energies which superseed the hadronic (multi-meson) channels as
well as the correlated and uncorrelated semi-leptonic D-meson decays. The
dilepton production from the strongly interacting quark gluon plasma (sQGP)
becomes already visible at top SPS energies and more pronounced at RHIC and LHC
energies.
