This paper proposes models to determine aquaculture and fisheries' contribution to Gross Domestic Product (GDP), given that no internationally agreed methodology is yet available. These include input-output models (with mathematical formulae and numerical examples), as well as alternatives for data-poor environments such as the satellite account approach. This will contribute to reporting on the fisheries GDP measure (Indicator 14.7.1), which is part of the Sustainable Development Goals (SDGs) and 2030 agenda, as well as to establishing a formal methodology, standards and guidelines for measuring aquaculture and fisheries' economic contribution. The publication also looks at how to apply the evidence obtained to policy and planning at the national, regional and global level, and takes note of the numerous practical issues to be resolved. Supply and demand-side factors that affect the contribution notably need to be taken into account. Inclusion of a fisheries GDP measure in the SDGs therefore provides a timely opportunity to move this enterprise forward.