The Working Group to develop a toolkit to identify and quantify the sources of plastic pollution in the aquatic environment is established under the UNEP/EC project: Global: Identifying and quantifying plastic contaminant sources and leakages into the aquatic environment. The working group will be comprised of assessment experts, modellers and pollution control experts, and other professionals with technical knowledge on plastic pollution and modelling, including assessment experts from the river basin organisations/regional seas programmes with experiences in identifying and quantifying plastic pollutants entering the freshwater/marine environments. The meetings of the working group will be organised three times during the toolkit development -through either physical or online meetings-, but some work will also be conducted between the meetings. One more meeting will be organised during the application of the developed tool to get feedback from the application process to improve the toolkit. Members of the working group will be selected taking into consideration the areas of their expertise, regional balance and gender balance and ensuring that developing country situations are fully considered.