Growing evidence suggests that anthropogenic litter, particularly plastic, represents a highly pervasive and persistent threat to global marine ecosystems. Multinational research is progressing to characterise its sources, distribution, abundance and impacts so that interventions aimed at reducing future inputs can be developed. Here, two elements of Sarah’s PhD research at the University of Exeter and Plymouth Marine Laboratory will be presented. The first, a 10-year nationwide assessment of marine litter on British beaches whereby citizen-science beach clean data were analysed to better understand the composition, spatial distribution and temporal trends of coastal debris. The second, an investigation into the ingestion of microplastics (plastic <5mm in size) by marine mammals, using both captive animals to garner information on trophic transfer of microplastics, and animals that stranded around the British coast to examine the extent of microplastic ingestion in wild marine mammals.