The Namibian onshore deposits have now been almost continuously mined for nearly a century and, inevitably, diamond production from these placers is dwindling. The last two decades, therefore, have seen increasing geological research and prospecting in marine environments that have led to the establishment of a successful marine diamond mining operation. Nearly one half of Namibia's total annual production is mined from the sea and this proportion is set to increase in the years ahead. Geologists use geophysical techniques such as shallow seismics and side-scan sonar, together with analysis of sediment clasts recovered during sampling operations, to characterise the seabed and the overlying diamond placers. These placers lie in waters ranging from the surf zone near the coast to depths as great as 150 metres. Evidence to date suggests that the marine environments host the same complex range of beach-barrier, beach, deflation and aeolian systems seen onshore.