  We emphasize the central role played by the spectral function in the
description of hadrons in matter and discuss the applicability of the
quasiparticle concept to the propagation of hadrons in dense nuclear matter.
Theoretical and experimental results relevant for the in medium properties of
vector mesons and kaons are briefly reviewed. We also present novel results for
the $\rho$ and $\omega$ spectral functions in nuclear matter, deduced from a
coupled channel analysis of pion-nucleon scattering data.
