© 2016 International Communication Association. Why has fact-checking spread so quickly within U.S. political journalism? In the first field experiment conducted among reporters, we varied journalist exposure to messages that highlight either audience demand for fact-checking or the prestige it enjoys within the profession. Our results indicate that messages promoting the high status and journalistic values of fact-checking increased the prevalence of fact-checking coverage, while messages about audience demand were somewhat less successful. These findings suggest that political fact-checking is driven primarily by professional motives within journalism, a finding that helps us understand the process by which the practice spreads within the press as well as the factors that influence the behavior of journalists.