Lepton-pair production in nuclear collisions – past, present, future

The key results on lepton-pair production in ultra-relativistic nuclear collisions are shortly reviewed, starting at the roots of pp collisions in the seventies, and ending at the perspectives of the colliders RHIC and LHC. The presence is dominated by the recent precision results from NA60 at the CERN SPS, culminating in the first measurement of the in-medium ρ spectral function and the transverse flow of the associated thermal radiation. The seeming cut-off of the flow above the ρ may well be the first direct hint for thermal radiation of partonic origin in nuclear collisions. The major milestones in the theoretical developments are also covered.