Dilepton production in heavy-ion collisions is considered as one 
 of the best probes of the medium formed in these reactions. Once
 produced, the dilepton will escape the fireball and provide direct
 information on the electromagnetic spectral function in the medium.
 For low masses (M<1GeV) the emission rate is dominated by decays 
 of the rho-meson. I will discuss the general objectives underlying 
 these studies, as well as calculations of the in-medium rho 
 spectral function and its phenomenology in heavy-ion collisions. 
 The same framework is applied to rho photoproduction off nuclei as 
 measured at JLAB. The results suggest an interpretation in terms 
 of ``quark-hadron duality" in a hot and/or dense medium.