The seas and oceans of the world have for centuries presented a picture of an endless landscape, a huge section of the environment that man was largely ignorant of, presenting threats to the survival to those working with it, and was impossible to control. For previous generations, it was almost inconceivable that waste disposed of in the seas could seriously affect them. In many ways the history of marine pollution is the pinnacle of the principle o f ‘dilute and disperse’. This principle is behind other pollution control measures such as uncontained landfill sites and the tall-stacks policies of the 1950s and 1960s for controlling air pollution. The idea is that toxic or nuisance substances lose their harmful qualities if dispersed into an environment where they can become highly diluted. In small quantities this is not unreasonable. However, as discharges increase in quantity, the principle breaks down. The sea was, for many years, viewed as an almost limitless location to dispose of and dilute waste from the land. However, we now realise that such discharges do pose serious threats to marine life and also to human health. The seas require protection, but many of the scientific and regulatory issues for a pollution manager are significantly more complicated than they are for the atmospheric or freshwater environment.