Reporters and fact-checkers are familiar with the challenges posed by rumors: They tend to be persistent. They are often entertaining. And they sometimes turn out to be true. Today, information often flies faster than facts can be known, as audiences on social networks share the claims, links, and memes that intrigue or outrage them. This is not limited to political content, of course, but it can be particularly impactful in certain domains — such as elections, where confidence in the process, and the outcome, is critical to democracy. Decades of research provide insight into how and why rumors spread, and this knowledge can help us anticipate what kinds of rumors might emerge and which rumors have the potential for virality.