Oceans cover 70% of our planet, provide 90% by volume of its biosphere, support 50% of global primary production and provide vital ecosystem services, including climate regulation, carbon sequestration and the provision of protein, on which large proportions of the global population rely. The Earth’s oceans are, however, increasingly subject to multiple interacting anthropogenic stressors. At the global scale, ocean acidification and global warming, considered two of the 21st century’s grand challenges, potentially pose the greatest threat to ecosystems and the goods and services they provide. However, regional scale stressors, such as eutrophication and over-fishing, are interacting with these global scale stressors, leading to non-linear ecosystem responses. To date, there is little understanding of the combined impacts of these stressors on marine organisms or the processes that structure marine ecosystems. The proposed research seeks to directly address this knowledge gap by undertaking a series of novel, integrated, robust manipulative experiments, at a hierarchy of spatial (local to global) and temporal scales (short to medium term), to determine the combined impacts of multiple climate (global warming and ocean acidification) and non-climate (eutrophication) stressors on marine biodiversity, community interactions and ecosystem functioning. Outcomes from this research will provide the first quantitative evidence of how multiple, interacting global environmental change stressors will affect the strength and direction of biotic interactions, ecosystem functioning and through interdisciplinary collaborations, changes to food-web dynamics and the economic sustainability of our oceans. Without a multi-species, ecosystem-level understanding of marine biological responses to global environmental change, adaptive management policies that are so vitally needed to ensure the sustained use of the Earth’s marine resources, will not be fit-for-purpos