Why do some of the richest fishing grounds on Earth collapse, even when everyone agrees the fish are valuable? The answer lies not in biology alone, but in a powerful economic force: when nobody owns the fish, nobody has an incentive to leave enough in the water for tomorrow. This chapter shows how blending simple population models with economic logic can explain overfishing—and, more importantly, how to design rules that turn a race to depletion into a long-term, profitable fishery.