  We address several aspects of gluon propagation at zero and finite
temperature. In particular, we study the violation of spectral positivity, we
discuss a method to extract the K\"all\'{e}n-Lehmann spectral density of a
particle (be it elementary or bound state) propagator and apply it to compute
gluon spectral densities from lattice data. Furthermore, we also consider the
interpretation of the Landau gauge gluon propagator at finite temperature as a
massive type bosonic propagator.
