Fact-checking has a traditional meaning in journalism that relates to internal procedures for verifying facts prior to publication, as well as a newer sense denoting stories that publicly evaluate the truth of statements from politicians, journalists, or other public figures. Internal fact-checking first emerged as a distinct role in U.S. newsmagazines in the 1920s and 1930s, decades in which the objectivity norm became established among American journalists. While newspapers have not typically employed dedicated fact-checkers, the term also refers more broadly to verification routines and the professional concern with factual accuracy. Both scholars and journalists have been concerned with a decline of internal fact-checking resources and routines in the face of accelerated publishing cycles and the economic crisis faced by news organizations in many parts of the world. External fact-checking consists of publishing an evidence-based analysis of the accuracy of a political claim, news report, or other public text. Organizations specializing in such “political” fact-checking have been established in scores of countries around the world since the first sites appeared in the United States in the early 2000s. These outlets may be based in established news organizations but also “good government” groups, universities, and other areas of civil society; practitioners generally share the broad goals of helping people become better informed and promoting fact-based public discourse. A burgeoning area of research has tried to measure the effectiveness of various kinds of external fact-checking interventions in countering misinformation and promoting accurate beliefs. This literature generally finds that fact-checking can be effective in experimental settings, though the influence of corrections is limited by the familiar mechanisms of motivated reasoning.