The Baseball color line was the unwritten policy which excluded African American baseball players from Organized Ball in the United States before 1947. As a result, various Negro Leagues were formed, which featured those players not allowed to participate in the major or minor leagues.

The separation's beginnings occurred in 1868, when the National Association of Baseball Players decided to bar "any club including one or more colored persons." As baseball became a professional sport, professional players were no longer restricted by this rule, and for a short while around 1890, African American players played in the big leagues. Over time, they were slowly excluded more and more. As prominent players such as Cap Anson, John McGraw, and Ty Cobb steadfastly refused to take the field with or against teams with African-Americans on the roster, it became informally accepted that African-Americans were not to participate in Major League Baseball.

The Negro National League was founded in 1920 by Rube Foster. This created two parallel major leagues, and until 1947, professional baseball in the United States was played in separate homogenous leagues.

During his term in office as the first baseball commissioner, Kenesaw Mountain Landis has been alleged to have been particularly determined to maintain the segregation. It is possible that he was guided by his background as a federal judge, and specifically by the then-existing constitutional doctrine of "separate but equal" institutions. He himself maintained for many years that black players could not be integrated into the major leagues without heavily compensating the owners of Negro League teams for what would likely result in the loss of their investments. In addition, integration at the major league level would likely have necessitated integrating the minor leagues, which were much more heavily distributed through the rural U.S. south and midwest.

In 1943, baseball executive Bill Veeck attempted to buy the Philadelphia Phillies franchise; rumors began circulating that he intended to purchase the contracts of several Negro Leaguers in order to make the longtime also-rans more competitive in a period when war requirements had depleted most rosters. However, the franchise was instead sold to a different ownership group, and some historians have recently questioned the likelihood of Veeck's rumored intentions.

The color line was formally breached when Branch Rickey, with the support of the new baseball commissioner, Albert "Happy" Chandler, signed the African American player Jackie Robinson in 1946, intending him to play for the Brooklyn Dodgers in the National League. After a year in the minor leagues, Robinson endured epithets and death threats and got off to a slow start in his first major league season in 1947, but his athleticism and skill earned him the Rookie of the Year award. Less well-known was Larry Doby, who signed with the Cleveland Indians that same year to become the American League's first African-American player. Both men were later elected to the Baseball Hall of Fame. Due to their success, teams slowly but surely integrated talented African-Americans on their roster.

The Boston Red Sox were the last team to integrate, signing Pumpsie Green in 1959.

See also

• History of baseball in the United States
• Negro League baseball
• List of First MLB Black Player by Team and Date