  The effects of the propagation of particles which have a finite life time and
an according width in their mass spectrum are discussed in the context of
transport descriptions. In the first part the coupling of soft photon modes to
a source of charged particles is studied in a classical model which can be
solved completely in analytical terms. The solution corresponds to a
re-summation of certain field theory diagrams. The second part addresses the
derivation of transport equations which also account for the damping width of
the particles. The $\Phi$-derivable method of Baym is used to derive a
self-consistent and conserving scheme. For this scheme a conserved
energy-momentum tensor can be constructed. Furthermore, a kinetic entropy can
be derived which besides the standard quasi-particle part also includes
contributions from fluctuation.
