  Understanding the infrared emission of galaxies is critical to observational
and theoretical investigations of the condensation of galaxies out of the
intergalactic medium and the conversion of gas into stars over cosmic time.
From an observational perspective, about half of all photons emitted within
galaxies are locally absorbed by dust grains, necessitating a self-consistent
analysis of the panchromatic emission of galaxies to quantify star-formation
and AGN activity as a function of epoch and environment. From a theoretical
perspective, physical processes involving dust are expected to play a major
role in regulating the accumulation of baryons in galaxies and their
condensation into stars on scales ranging from Mpc down to sub-pc. All this
requires a quantitative analysis of the interaction between dust, gas and
radiation. Here we review progress in the modelling of some of these processes.
