It is widely recognised that marine litter can have significant ecological, social and economic impacts. Plastics form a large proportion of marine litter, and the widespread occurrence of macroscopic plastic debris and the direct impact this can have both on marine fauna and legitimate uses of the environment, sometimes remote from industrial or urban sources, has been well documented. Plastic debris comes in a wide variety of sizes and compositions and has been found throughout the world ocean, carried by ocean currents and biological vectors (e.g. stomach contents of fish, mammals and birds). Plastics degrade extremely slowly in the open ocean, partly due to UV absorption by seawater and relatively low temperatures. In recent years the existence of micro-plastics and their potential impact has received increasing attention. The IOC is leading global efforts to understand the sources, fate and effects of plastics and microplastics in the marine environment. Together with the United Nations Environment Programme (UNEP), it coordinates Working Group 40 on Plastics and Micro-plastics in the Ocean of the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP).