  It is well established in the local Universe that regions of high
star-formation rate are dusty. As a result of this physical causal link,
galaxies of increasing current star formation activity emit a larger proportion
of their bolometric luminosity via dust absorption and re-radiation in the
thermal mid- to far-infrared. Several new observations indicate that this trend
continues back to earlier cosmic times, when star formation rates were very
high, and a large fraction of the resulting UV power was reprocessed by dust
into the infrared. For studying the more luminous, (and therefore more dusty)
galaxies, infrared spectroscopy is crucial even at moderate redshifts. For the
less dusty galaxies, we are still driven strongly to longer wavelengths as
their redshifts increase from 5 to 10. On the observational side, infrared
astronomy is about to start catching up with optical astronomy in sensitivity,
spatial resolution and field-of-view. Therefore, long-wavelength observations
will play the key role in our understanding of galaxy formation and evolution
in the ``Immature Universe."
