People used to hold out great hope for a public square in which individuals put petty disputes aside and engage in rational discussion about important issues. Unfortunately, public discourse today—especially on the internet—is full of adults behaving like poorly socialized children, acting out to show off for people they want to impress. In short, they engage in moral grandstanding, or the use of moral talk for self-promotion. Drawing from work in psychology, economics, and political science, this book develops an explanation of why people grandstand when they talk about morality and politics. Using the tools of moral philosophy, it argues that grandstanding is not just annoying, but morally bad. And finally, it explains what we can do to encourage people to support a public square worth participating in, by avoiding grandstanding.