Abstract: Much of the time, human beings do what others do. This is perfectly sensible, because the actions and statements of other people convey valuable information about what should be done. In addition, most people want the good opinion of others, and this desire promotes conformity. But conformity can lead both groups and institutions in unfortunate and even catastrophic directions. The most serious problem is that by following others, people fail to disclose what they know and believe, thus depriving society of important information. Those who dissent, and who reject the pressures imposed by others, perform valuable social functions, often at their own expense, material or nonmaterial. These points are illustrated by reference to theoretical and empirical work on conformity, cascades, and group polarization. An understanding of the role of conformity and dissent casts new light on a variety of legal issues, including the expressive function of law; the institutions of the American constitution; the functions of free speech in wartime; the debate over the composition of the federal judiciary; and affirmative action in higher education.