Social Media and the Public Interest explores how and why social media platforms became so central to news consumption and distribution as they met many of the challenges of finding information―and audiences―online. Napoli illustrates the implications of a system in which coders and engineers drive out journalists and editors as the gatekeepers who determine media content. He argues that a social media–driven news ecosystem represents a case of market failure in what he calls the algorithmic marketplace of ideas. To respond, we need to rethink fundamental elements of media governance based on a revitalized concept of the public interest. A compelling examination of the intersection of social media and journalism, Social Media and the Public Interest offers valuable insights for the democratic governance of today’s most influential shapers of news.