Description: Digital twins are fine-grained digital replicas of physical objects and systems which have been widely applied in the engineering realm for tasks such as engine optimization and port management. Recently, digital twins have also caught the attention of marine scientists as a solution to socio-environmental problems. By bundling and providing access to observational data, models, and simulations, digital twins allow users to explore current and future ‘what-if’ scenarios, especially related to human interactions with the ocean. High-value application areas include fisheries and mariculture, marine protected areas, ocean-based tourism, ecological forecasting, nature-based solutions, marine infrastructure development, and the interactions between all of these with an ever-growing collection of data streams.In the context of the UN Decade of Ocean Science for Sustainable Development, we launched the international programme “DITTO - The Digital Twins of the Ocean“ (ditto-oceandecade.org) in May 2022. DITTO’s mission is to develop and share a common understanding of Digital Twins of the Ocean, to establish best practice examples and to advance a digital framework to empower ocean professionals to effectively create their own application-focused digital twin. This powerful framework will enable users to visualize and explore ocean knowledge and empower ocean professionals and models, forecasts, citizen scientists, policymakers, and the general public alike.A successful regional implementation of a Digital Twin depends on four aspects: A) a capable ocean observing system B) An innovative ocean modeling and prediction capability C) An interoperable, shared and easily accessible data environment. D) An interactive user interface. International cooperation will be key for success.