Why do many oppose the selling of human organs if, as economists argue, this would increase supply? Economists see material incentives as key to changing behaviour – and are puzzled if incentives don’t work as expected. For psychologists, social norms explain such behaviour; legal scholars say law can shape society’s norms. CEPR DP8663 tries to reconcile these disparate insights with a unifying theory that could explain puzzles such the aversion to organ-selling as well as why so many people resist economists’ advice.