This report is a contribution to the Strategic Environmental Assessment (SEA5) conducted by the Department of Trade and Industry (now Department of Energy and Climate Change). Cephalopods are short-lived molluscs, characterised by rapid growth rates, and are important predators and prey in oceanic and neritic environments. They can range in size from 1.5 cm in pygmy squid (Sepiolidae) to 20 m in giant squid (Architheutidae). Cephalopods exhibit the highest degree of development in invertebrate nervous systems, expressed through complex behaviour patterns such as the ability to learn and the display of complex colour changes. In contrast to other molluscs, most cephalopods lack an external shell, are highly mobile as adults and occupy similar ecological niches to predatory fish. This report focuses mainly on the species of fishery importance: the loliginid squid Loligo forbesi and the ommastrephid squid Todarodes sagittatus and Todaropsis eblanae together with the octopus Eledone cirrhosa. Brief accounts of other commonly occurring cephalopod species are also provided.