Who owns the sea? About 40% of the world's population lives in coastal communities and depend on ocean resources. Yet over the twentieth century governments and corporations around the world have pushed the fatally flawed maxim of 'blue growth', and as a result nearly all fish stocks are either fully or over-exploited. In the neoliberal era, it has been extensively enclosed and privatized, generating multiple inequalities. A system of rentier capitalism now dominates human activity in the sea, based on privatization, financial capital and a drive for profit over people and ecosystems. Substantial and detailed, The Blue Commons peels back the veil of the boundless exploitation and corruption. From an economist who has been responsible for much of our contemporary understanding of inequality, and one of the greatest modern thinkers of possible solutions, the scale of the problem in our oceans is revealed here for the first time, as well as our one solution for reversing it: building a blue commons alternative, prioritizing ordinary people around the world and the health of our oceans.