Joseph Jefferson Jackson (July 16, 1887 – December 5, 1951), nicknamed "Shoeless Joe", was an American professional baseball outfielder who played in Major League Baseball (MLB) in the early 20th century. His .356 career batting average is one of the highest in major-league history. Jackson is often remembered for his association with the Black Sox Scandal in which eight members of the 1919 Chicago White Sox participated in a conspiracy to fix the World Series. As a result, Commissioner Kenesaw Mountain Landis permanently banned Jackson and the other seven players from professional baseball after the 1920 season. During the World Series in question, Jackson had led both teams in several statistical categories and set a World Series record with 12 base hits, including, during the last game, the only home run in that World Series. Jackson's role in the scandal, banishment from the game, and exclusion from the Baseball Hall of Fame have been fiercely debated. In 2025, Commissioner Rob Manfred removed Jackson and other deceased players from the MLB's permanently ineligible list, thus lifting the ban.

Jackson played for three MLB teams during his 12-year career, primarily in left field. He spent 1908–1909 as a member of the Philadelphia Athletics and 1910 with the minor league New Orleans Pelicans before joining the Cleveland Naps at the end of the 1910 season. He was still considered a rookie in 1911 when he hit for a .408 average, a single-season record for a rookie that still stands. He remained in Cleveland until early in the 1915 season; he then played for the White Sox through 1920. Later, Jackson played baseball under assumed names throughout the South.

Jackson holds the now Cleveland Guardians and Chicago White Sox franchise records for triples in a season and career batting average. In 1999, he ranked number 35 on The Sporting News' list of the 100 Greatest Baseball Players and was a finalist for the Major League Baseball All-Century Team. The fans voted him as the 12th-best outfielder of all time. He also ranks 33rd on the all-time list for non-pitchers according to the win shares formula developed by sabermetrician Bill James. Baseball legend Babe Ruth said that he modeled his hitting method after Jackson's.

Jackson was born in Pickens County, South Carolina, the oldest son of George Jackson, a sharecropper. While Jackson was still a baby, his father moved the family to Pelzer, South Carolina. A few years later, the family moved to a company town called Brandon Mill on the outskirts of Greenville, South Carolina. An attack of measles almost killed him when he was 10. He was bedridden for two months and paralyzed while he was nursed back to health by his mother.

Starting at the age of 6 or 7, Jackson worked in one of the town's textile mills as a "linthead", a derogatory name for a mill hand. Family finances required Jackson to take 12-hour shifts in the mill, and since education at the time was a luxury the Jackson family couldn't afford, Jackson was functionally illiterate. His lack of education ultimately became an issue throughout Jackson's life. It even affected the value of his memorabilia in the collectibles market; because Jackson was illiterate, he often had his wife forge his signature. Consequently, anything provably autographed by Jackson himself brings a premium when sold, including one autograph which was sold for $23,500 in 1990 (equivalent to $57,000 in 2024). In restaurants, rather than ask someone to read the menu to him, he would wait until his teammates ordered and then order one of the items that he heard.

In 1900, when he was 13 years old, his mother was approached by one of the owners of the Brandon Mill, and he started to play for the mill's baseball team. He was the youngest player on the team. He was paid $2.50 to play on Saturdays (equivalent to $94 in 2024). Jackson was initially a pitcher, but one day he accidentally broke another player's arm with a fastball. No one wanted to bat against him, so the team manager placed him in the outfield. Jackson's hitting ability made him a celebrity around town. Around that time, he was given a baseball bat that he named Black Betsy. He was compared to Champ Osteen, another player from the mills who made it to the majors. Jackson moved from mill team to mill team in search of better pay, playing semi-professional baseball by 1905.

In an interview published in the October 1949 edition of Sport magazine, Jackson recalled that he got his nickname during a mill game played in Greenville, South Carolina. Jackson had blisters on his foot from a new pair of cleats, which hurt so much that he took his shoes off before he was at bat. As play continued, a heckling fan noticed Jackson running to third base in his socks and shouted, "You shoeless son of a gun, you!" and the resulting nickname "Shoeless Joe" stuck with him throughout the remainder of his life.

In 1908, Jackson began his professional baseball career with his hometown minor league team, the Greenville Spinners of the Carolina Association, married 15-year-old Katie Wynn, and eventually signed with Connie Mack to play for the Philadelphia Athletics.