  We present illustrative models for the UV to millimeter emission of starburst
galaxies which are treated as an ensemble of optically thick giant molecular
clouds (GMCs) centrally illuminated by recently formed stars. The models follow
the evolution of the GMCs due to the ionization-induced expansion of the HII
regions and the evolution of the stellar population within the GMC according to
the Bruzual & Charlot stellar population synthesis models. The effect of
transiently heated dust grains/PAHs to the radiative transfer, as well as
multiple scattering, is taken into account.
  The expansion of the HII regions and the formation of a narrow neutral shell
naturally explains why the emission from PAHs dominates over that from hot dust
in the near to mid-IR, an emerging characteristic of the infrared spectra of
starburst galaxies.
  The models allow us to relate the observed properties of a galaxy to its age
and star formation history. We find that exponentially decaying 10^7-10^8 yrs
old bursts can explain the IRAS colours of starburst galaxies. The models are
also shown to account satisfactorily for the multiwavelength data on the
prototypical starburst galaxy M82 and NGC6090, a starburst galaxy recently
observed by ISO. In M82 we find evidence for two bursts separated by 10^7yrs.
In NGC6090 we find that at least part of the far-IR excess may be due to the
age of the burst (6.4 x 10^7yrs). We also make predictions about the evolution
of the luminosity of starbursts at different wavelengths which indicate that
far-IR surveys may preferentially detect older starbursts than mid-IR surveys.
