As online news and social media have proliferated over the last decade, a whole new category of information has entered the popular lexicon: fake news. Online disinformation has come a long way from “On the Internet, nobody knows you're a dog” to a place where a malicious article hatched from a troll farm can sit side-by-side with legitimate, rigorous journalism. Awareness of the issue is widespread, but stopping misinformation requires social media platforms, journalists, fact checkers, and citizens all to take action.