Due to growing demands and high metal prices, the mineral resources of the oceans have become an attractive target for the international mining industry. Heavy mineral deposits in coastal areas, cobalt crusts at the slopes of seamounts, manganese nodules in sediment-covered deep-sea basins, and massive sulfide deposits at ocean spreading ridges contain vast amounts of metals that are of potential interest to the world economy. Off-shore heavy mineral deposits enriched in chromite, titanium and tin are known in many parts of the world oceans, however, only diamonds are currently being mined on an industrial scale off the coasts of Namibia and South Africa at water depths up to 150m. Cobalt-rich and platinum-bearing manganese crust have been explored in the Pacific Ocean where they occur at the flanks of seamounts at water depths of about 800-1.500m. However, mining of cobalt crust has shown to be difficult as the crusts are intimately associated with underlying substrate rocks from which they have to be broken off for recovery. Manganese nodules mainly occur on top of semi-consolidated sediments at water depths of 5.000-6.000m in the Pacific and Indian Oceans, where they cover large areas of the seafloor. The main interest in manganese nodules results from the fact that they contain certain amounts of nickel, copper, and cobalt in addition to some rare elements. However, mining of manganese nodules will likely cause a significant disturbance of fine-grained sediments that, due to bottom currents, will be transported over large areas of the Pacific seafloor. Such a “dust storm” in the Pacific created by manganese nodule mining would have a major impact on life in the deep-sea and cannot be tolerated from the environmental point of view. Black smokers and massive sulfide deposits that are rich in base (copper, zinc, lead), precious (gold, silver), and rare metals such as indium have been first discovered in 2.600m water depth at the East Pacific Rise in 1979. Over the past 30 years, more than 400 new deposits of this type have been discovered along the world ocean spreading ridges. Many of the deposits are located within the 200 nautical miles Exclusive Economic Zone of coastal states which has resulted in the fact that a number of countries have already granted exploration licences for their territorial waters to international mining companies. Mining of inactive seafloor massive sulfide deposits at volcanic ocean ridges appears to be environmentally feasible, as mining activities would only impact a relatively small area of the seafloor. Mining technology for seafloor massive sulfide mining basically exists and locally high concentrations of valuable metals are likely to make mining of these deposits economically feasible. However, systematic drilling of individual deposits is required in order to arrive at reliable estimates of grades and tonnages. Given the current industry interest in seafloor massive sulfide deposits, it is expected that the recovery of metals from a deposits within the territorial waters of Papua New Guinea will become reality within the next five years.