  A cosmologically significant population of very luminous high-redshift
galaxies has recently been discovered at submm wavelengths. Advances in submm
detector technologies have opened this new window on the distant Universe. Here
we discuss the properties of the high-redshift submm galaxies, their
significance for our understanding of the process of galaxy formation, and the
selection effects that apply to deep submm surveys. The submm galaxies generate
a significant fraction of the energy output of all galaxies in the early
Universe. We emphasize the importance of studying a complete sample of submm
galaxies, and stress that because they are typically very faint in other
wavebands, these follow-up observations are very challenging. Finally, we
discuss the surveys that will be made using the next generation of submm-wave
instruments under development.
