Study abstract: The Internet has democratized access to information but in so doing has opened the floodgates to misinformation, fake news, and rank propaganda masquerading as dispassionate analysis. To investigate how people determine the credibility of digital information, we sampled 45 individuals: 10 Ph.D. historians, 10 professional fact checkers, and 25 Stanford University undergraduates. We observed them as they evaluated live websites and searched for information on social and political issues. Historians and students often fell victim to easily manipulated features of websites, such as official-looking logos and domain names. They read vertically, staying within a website to evaluate its reliability. In contrast, fact checkers read laterally, leaving a site after a quick scan and opening up new browser tabs in order to judge the credibility of the original site. Compared to the other groups, fact checkers arrived at more warranted conclusions in a fraction of the time. We contrast insights gleaned from the fact checkers’ practices with common approaches to teaching web credibility.