Digital Twins of the Ocean (DTOs) are emerging as a new paradigm for integrating ocean observations, numerical models, data assimilation, artificial intelligence and interactive digital environments. Their development reflects substantial progress in observing technologies, high-resolution modelling, interoperable data infrastructures and computational capabilities. However, DTO maturity remains heterogeneous, and the transition from innovative prototypes to reliable systems supporting operational decisions is still incomplete.

This contribution examines the current development of DTOs across the full information value chain, from sustained and adaptive observations to prediction, scenario exploration and decision support. Recent advances demonstrate an evolution from individual digital components towards integrated and continuously updated systems. These systems increasingly combine satellite and in situ observations, autonomous platforms, physical and biogeochemical models, hybrid physics–AI approaches, cloud and high-performance computing, and user-oriented interfaces. Applications now address coastal hazards, marine heatwaves, ecosystem change, pollution, fisheries, aquaculture, offshore activities and climate adaptation.

The analysis also identifies critical scientific and implementation challenges. These include validation and uncertainty quantification, interoperability across platforms and spatial scales, transparent data and model provenance, long-term operational sustainability, and the integration of ecological, socioeconomic and governance dimensions. Unequal access to observations, computational infrastructure, expertise and financial resources further limits the development and use of DTOs in many regions.

DTOs should therefore be understood not as a single technology or a technological solution in themselves, but as evolving socio-technical systems connecting scientific knowledge with user needs and decision processes. Their contribution will depend on rigorous evaluation, fit-for-purpose design, sustained co-development and credible evidence of decision impact. A common framework for assessing DTO maturity and documenting their global development would help identify remaining gaps, support interoperability and guide investment. Advancing these foundations is essential for transforming DTO innovation into trusted and actionable knowledge for sustainable ocean management.