The world’s battered oceans are the poster child of humanity’s neglect of our home planet. We desperately need effective transnational institutions to protect the global commons—oceans, the climate system, biodiversity, etc.—but have failed to build them. This governance vacuum has become a breeding ground of degradation. The oceans, for instance, suffer from a toxic mix of overfishing, pollution, acidification, and warming waters. Critical marine species have declined by some 50% over the last two decades, with the risk of crossing ecological tipping points looming larger with each passing year. The scope of such a calamity could be huge: millions of people depend on healthy oceans for their livelihood, and the economic value generated by the oceans stands at some $2.5 trillion per year. The complexity of ocean ecosystems demands a holistic strategy, not piecemeal solutions. State-centric efforts to date have been too fragmented and toothless. We urgently need an upwelling of political will—and a popular movement to demand it—if we are to act collectively to save the oceans and the common treasury of Earth.