  An introduction to physics of in-medium hadrons with special emphasis towards
modification of vector meson properties in dense nuclear matter is given. We
start from remarkable analogy between the in-medium behavior of atoms in gases
and hadrons in nuclear matter. Modifications of vector meson widths and masses
can be registered experimentally in heavy-ion collisions by detecting dilepton
spectra from decays of nucleon resonances and light unflavored mesons including
$\rho$- and $\omega$-mesons. Theoretical schemes for description of the
in-medium hadrons are reviewed and recent experimental results of the NA60 and
HADES collaborations on the dilepton production are discussed.
