Pollution from human activities can be found at all points across the ocean’s vast expanse, whether in the deep, at the surface, or in the organisms that live in it. Rivers carry waste, solid and liquid, and a wide range of other substances into the ocean. Discharges, spills and waste from shipping are another source of pollution. Pollutants discharged into the air are deposited into the ocean. Although considerable progress has been achieved in limiting some forms of pollution, others persist. New challenges, whether relating to particular pollutants, such as micro-plastics, or broader trends, like the rapid growth of coastal cities, will require sustained action encompassing scientific research, knowledge-sharing, and strengthened governance arrangements.