  This contribution summarizes the main experimental results presented at the
2009 Quark Matter conference concerning single and dilepton production in
proton and heavy ion collisions at high energy. The dilepton invariant mass
spectrum has been measured over a range that extends from the $\pi^0$ mass to
the $\Upsilon$ mass, and for various collision energies at SPS, Fermilab, Hera
and RHIC. This paper focuses on the various contributions (photons, low mass
vector mesons, open and hidden heavy flavors) to this spectrum and discuss
their implications on our understanding of the matter formed in heavy ion
collisions.
