We conduct our work in twenty Case Studies. Fourteen of them are on a regional scale while six are pan-European. All Case Studies are designed to deliver a cause-and-effect understanding, to build predictive capacity in models, and to develop indicators and tools for decision-makers charged with the stewardship of European marine biodiversity under threats from multiple drivers. In each case, drivers examined represent the local/regional priorities from regulators who co-create what-if scenarios of interacting drivers including envisioned management actions. Our Case Studies cover eight European seas and three climatic zones.