This report provides a review of 19 existing and emerging methodologies as of early 2019 that identify the abundance, distribution, types, sources, pathways and sinks of plastic pollution at different scales. It also provides an overview of the state of knowledge for impact assessment and monetary valuation methodologies, along with a glossary of key terms related to plastics, marine plastics, and environmental footprints. This publication highlights gaps in current methodologies including assessing impacts in a comprehensive manner that allows for measurement of trade-offs between different impacts. This report's conclusions lay a solid foundation for the development of a standardized and replicable plastic environmental footprint measurement tool and a standard set of indicators that highlight the costs of inaction.