This assessment describes the far-reaching impacts of plastics across the planet and in our oceans. The assessment sets out to address four key questions to help guide future actions: • What can new research and evidence tell us about the environmental and human health effects and impacts of marine litter, including plastics and microplastics? • What is the latest understanding of the sources, pathways, behaviour and fate of marine litter, especially plastics? • What are the most effective field, laboratory and modelling approaches for monitoring and measurement of the sources, pathways, behaviour and fate of marine litter, including all sizes of plastics? • What ongoing responses and actions, environmental technologies and business solutions exist to tackle this urgent global problem?