Global marine capture fisheries are an underperforming global asset. The Sunken Billions study shows that the difference between the potential and actual net economic benefits from marine fisheries is in the order of $50 billion per year – equivalent to more than half the value of the global seafood trade. The cumulative economic loss to the global economy over the last three decades is estimated to be in the order of two trillion dollars. In many countries the catching operations are buoyed up by subsidies, so that the global fishery economy to the point of landing (the harvest sub-sector), is in deficit. Improved governance can recapture a substantial proportion of the of this $50 billion annual economic loss. With effective economic incentives, rather than being a net drain on the global economy, sustainable fisheries can create an economic surplus, be a driver of economic growth and a basis for livelihood opportunities. Economically, healthy fisheries are fundamental to achieving not only the restoration of fish stocks but other accepted objectives for the fisheries sector, such as improved livelihoods, exports, fish food security and economic growth. When fish stocks are fully exploited in the biological sense, the associated fisheries are almost invariably performing below their economic optimum. In some cases, fisheries may be biologically sustainable but still operate at an economic loss. The depletion in fish capital resulting from overexploitation is rarely reflected in the reckoning of a nation's overall capital and GDP growth. For over three decades the world's marine fish stocks have come under increasing pressure from fishing, from loss of habitats and from pollution. Rising sea temperatures and the increasing acidity of the oceans is placing further stress on already stressed ecosystems. Illegal fishing and unreported catches undermine fishery science while some subsidies continue to support unsustainable fishing practices. Marine fisheries reform can recapture a substantial proportion of the economic losses. Rather than being a net drain on the global economy, sustainable fisheries can create an economic surplus and be a driver of economic growth, both in the marine economy and other sectors. The biological sustainability of fish stocks has often occupied the centre stage of international efforts, for example, the Plan of Implementation of the WSSD makes specific reference to recovery of fish stocks. However sustainable fisheries are not only a problem of biology and ecology, but one of managing political and economic processes and replacing pernicious incentives with those which foster improved governance and responsible stewardship. The comprehensive reforms required imply political, social and economic costs. Fisheries reform is a long-term process and will require political will founded on a consensus vision built through broad stakeholder dialogue.