  Recent developments on medium modifications of hadron properties in dense and
hot hadronic matter are discussed. I will focus in particular on the behavior
of spectral functions associated to collective scalar-isoscalar modes, kaons
and vector mesons from ordinary nuclear matter to highly excited matter
produced in relativistic heavy-ion collisions from SIS to SPS energies. Various
theoretical approaches are presented in connection with the interpretation of
experimental data. Special emphasis will be put on the role of chiral dynamics
and chiral symmetry restoration. I will discuss in particular to which extent
the broadening of the rho meson peak signals the onset of chiral symmetry
restoration.
