Marine plastics, and their potential environmental impacts, have seen an explosion in research and public interest over the last 5 years. Plastic debris is now found globally, from the poles to the deepest ocean trenches, and we are only just starting to understand the processes by which plastics move through and break down in the environment and their implications for planetary health. This lecture will discuss the amounts and sources of plastics reaching the oceans, and (focusing on microplastics) the processes by which they may be trapped and accumulate in river and coastal environments, their potential impacts, current knowledge gaps, and methods of reducing the ocean plastic burden.