Nobel Prize winner Alvin Roth argues that our most important and difficult decisions - about our most controversial issues - require a different calculation of what matters most.Our intuitive and automatic thinking is influenced - in ways we don't always recognize - by strongly-held notions of repugnance. A transaction is repugnant if some people want to engage in it, and others think they shouldn't be allowed to. You Can't Do That explores how ideas about repugnance have changed drastically over time, and examines the causes and consequences of forbidding transactions in our most intimate relationships (such as sex, reproduction, or donating blood) and our commercial relationships (finance, labor, or data use).Leading economist Alvin Roth turns his attention to a controversial set of markets to answer difficult questions about allowing, regulating or forbidding certain transactions. Should narcotics be legalised? Should we allow compensation for kidney donors, or let thousands of people die each year while waiting for an altruistic kidney? Should we allow physician-assisted suicide for terminally ill patients who desire death with dignity? Roth's goal is not to tell us what to think, but to give us a new framework for how to think - balancing the rights of people to pursue their individual and mutual goals with the need to protect society's most vulnerable members from harms that might arise from markets, including black markets, growing without boundaries.This is about trade-offs, not moral absolutes. Combining Roth's expertise in market design with his skill in making complicated ideas accessible, You Can't Do That examines how to make those trade-offs in the most humane, beneficial, and efficient ways.