This policy brief addresses the challenge of monitoring plastic pollution in the context of the Global Plastics Treaty. It was developed by members of the Scientists’ Coalition for an Effective Plastics Treaty. All of the policy briefs within this series are published on Zenodo and can be found within the Coalition’s Zenodo Community: https://zenodo.org/communities/scientists_coalition/ More information about the Coalition (including contact information) is available on its website: https://scientistscoalition.org