  Optical/UV photons and even harder radiation components in galaxies are
absorbed and scattered by dust and re-emitted at infrared wavelengths. For a
better understanding of the obscured regions of the galaxies detailed models of
the interaction of photons with dust grains and the propagation of light are
required. A problem which can only be solved by means of numerical solution of
the radiative transfer equation. As a prologue we present high angular mid IR
observations of galactic nuclei in the spirit of future ELT instrumentation.
Dust models are discussed, which are suited to fit the extinction curves and
relevant to compute the emission of external galaxies. Self-consistent
radiative transfer models have been presented in spherical symmetry for
starburst nuclei, in two dimensions for disk galaxies (spirals) and, more
recently, in three dimensional configuration of the dust density distribution.
For the latter, a highlighting example is the clumpy dust tori around AGN.
Modern advances in the field are reviewed which are either based on a more
detailed physical picture or progress in computational sciences.
