ACTNOW advances the state-of-the-art in understanding and forecasting of the cumulative impacts of climate change and interacting drivers on marine systems. The program provides solutions options to halt the loss of biodiversity, to restore and protect habitats and ecosystem processes, and to safeguard the contributions of marine areas to human well-being. ACTNOW is co-developed with EU policy stakeholders to deliver: 1) Mechanistic (cause-and-effect) understanding of the impacts of multiple interacting drivers on organisms, communities, habitats and ecosystems from individual-level performance to ecosystem-level stability, resistance, resilience and tippingpoints; 2) Improved monitoring and new indicators of marine biodiversity based on state-of-the-art biologging technology, molecular methods and advanced numerical modeling; 3) Enhanced forecasts of European marine biodiversity, ecosystem functioning and services using scenarios (co-created and regionalized with practitioners) of multiple drivers and management settings, as well as integrated impact assessment methods; 4) Fit-for-purpose decision-support tools enabling regulators to deliver regionally-appropriate assessments and actions to restore and maintain Good Environmental Status; 5) Next-generation training for early-career scientists working on solutions to the dual crises of biodiversity loss and climate change and capacity building to enhance public literacy on the One Health concept. ACTNOW builds predictive capacity of multiple driver effects and performs integrated indicators assessments of biodiversity across 20 Case Studies capturing all European climate zones and regional seas, including pan-European research on key groups in marine food webs. dies capturing all European climate zones and regional seas, including pan-European research on key groups in marine food webs.