Jackie Robinson Day is a traditional event which occurs annually on April 15 in Major League Baseball (MLB), commemorating and honoring the day Jackie Robinson made his major league debut. Celebrated at MLB ballparks, on that one day, all players, coaches, and managers on both teams, and the umpires, wear Robinson's uniform number, 42. April 15 was Opening Day in 1947, Robinson's first season in the major leagues.

Jack Roosevelt Robinson was an American professional baseball player who became the first African American to play in Major League Baseball (MLB) in the modern era. Robinson broke the color line when he started at first base for the Brooklyn Dodgers on April 15, 1947. The Dodgers signing Robinson heralded the end of racial segregation in professional baseball that had relegated black players to the Negro leagues since the 1880s. Robinson was inducted into the Baseball Hall of Fame in 1962.