Compared with conventional land-based mining and processing operations, the exploitation of minerals from the seabed, particularly in deep water, involves a vast range of new problems in conducting the various stages of mining, transportation, processing and disposal of waste products, in a marine environment. In all such operations the ways in which local sea and weather conditions and their seasonal variations affect the stability of the vehicle, be it ship or other floating structure or submersible from which the operations are being conducted, have to be taken into account. The resulting motion together with vibration generated by propulsion and other machinery are significant factors in the performance and behaviour of equipment and materials during processing, handling and transportation operations at sea. In deep-sea mining operations at depths of 2-5 km the effects of associated pressure, salinity and temperature must also be dealt with. The paper reviews the present state of such knowledge as currently practised in continental-shelf operations, and as proposed in various deep-sea mining operations. Associated research requirements for future mineral exploitation in the deep-sea environment are discussed.