Robinson's jersey number, 42, was retired by Major League Baseball; no future player on any major league team can wear it. The number was retired in ceremonies at Shea Stadium to mark the 50th anniversary of Robinson's first game with the Dodgers.
A handful of players who wore number 42 as a salute to Robinson, such as the Mets' Butch Huskey and Boston's Mo Vaughn, were allowed to continue to use the number. The Yankees' Mariano Rivera is the last player in the major leagues to wear jersey number 42 on a regular basis.
As an exception to the retired-number policy, Major League Baseball has recently begun honoring Robinson by allowing players to wear number 42 on April 15, Jackie Robinson Day. For the 60th anniversary of Robinson's major league debut, Major League Baseball invited players to wear the number 42 on Jackie Robinson Day in 2007. The gesture was originally the idea of outfielder Ken Griffey, Jr., who sought Rachel Robinson's permission to wear the number. After receiving her permission, Commissioner Bud Selig not only allowed Griffey to wear the number, but also extended an invitation to all major league teams to do the same. Ultimately, more than 200 players wore number 42, including the entire rosters of the Los Angeles Dodgers, New York Mets, Houston Astros, Philadelphia Phillies, St. Louis Cardinals, Milwaukee Brewers, and Pittsburgh Pirates. The tribute was continued in 2008, when, during games on April 15, all members of the Mets, Cardinals, Washington Nationals, and Tampa Bay Rays wore Robinson's number 42. On June 25, 2008, Major League Baseball installed a new plaque for Robinson at the Baseball Hall of Fame commemorating his off-the-field impact on the game as well as his playing statistics.
In 2009, all uniformed personnel (players, managers, coaches, and umpires) wore number 42 on April 15.