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.