The Doubleday myth is the claim that the sport of baseball was invented in 1839 by future American Civil War general Abner Doubleday in Cooperstown, New York. In response to a dispute over whether baseball originated in the United States or was a variation of the British game rounders, the Mills Commission was formed in 1905 to seek out evidence. Mining engineer Abner Graves authored a letter claiming that Doubleday invented baseball. The letter was published in a newspaper and eventually used by the Mills Commission to support its finding that the game was of American origin. In 1908, it named Doubleday the creator of baseball.

The question of the origins of baseball has been the subject of debate and controversy for more than a century. Baseball and the other modern bat, ball, and running games – stoolball, cricket and rounders – were developed from folk games in early Britain, Ireland, and Continental Europe. Early forms of baseball had a number of names, including "base ball", "goal ball", "round ball", "fetch-catch", "stool ball", and, simply, "base". In at least one version of the game, teams pitched to themselves, runners went around the bases in the opposite direction of today's game, much like in the Nordic brännboll, and players could be put out by being hit with the ball. Just as now, in some versions a batter was called out after three strikes.