One of the key goals in observational cosmology over the next few years will be to establish the redshift distribution of the recently discovered sub-mm source population. In this brief review I discuss and summarize the redshift information which has been gleaned to date for the similar or equal to 50 bright sub-mm sources which have been uncovered via the six main classes of survey performed with SCUBA on the JCMT over the last 2-3 years. Despite the biases inherent in some of these surveys, and the crudeness of the redshift information available in others, I conclude that all current information suggests that only 10-15% of luminous sub-mm sources lie at z < 2, and that the median redshift of this population is z similar or equal to 3. I suggest that such a high median redshift is arguably not unexpected given current theories designed to explain the correlation between black-hole mass and spheroid mass found at low redshift. In such scenarios, peak AGN emission is expected to correspond to, or even to cause termination of major star-formation activity in the host spheroid. In contrast, maximum dust emission is expected to occur roughly half-way through the star-formation process. Given that optical emission from bright quasars peaks at z similar or equal to 2.5, dust-emission from massive ellipticals might be reasonably expected to peak at some point in the preceding similar or equal to 1 Gyr, at z similar or equal to 3. Confirmation or refutation of this picture requires significantly-improved redshift information on bright samples of SCUBA sources. (C) 2001 Elsevier Science B.V. All rights reserved.