Starting with the 81st All-Star Game on July 13 in Anaheim, the changes include:
The contest always will include a designated hitter no matter where it's played.
No starting pitcher who competes for his team on the previous Sunday will be allowed to pitch in the game.
Rosters have been increased to 34 players, by one slot designated for a position player.
A rule will allow one position player re-entry into the game if necessitated by injury.
The procedural changes, agreed upon by Major League Baseball and the Major League Baseball Players Association, come as the most significant alterations to the sport recommended by the Special Committee to date.
Chaired by Commissioner Bud Selig and composed of longtime managers, executives and observers of the game, the committee was formed in December. It previously recommended an off-day be removed from the League Championship rounds to tighten the playoff schedule, and the Commissioner's Office announced that change in March.
These also are the first significant alterations to the All-Star Game format since 2003, when the game was declared the deciding factor for which league hosts the World Series. That change, along with a roster bump from 30 to 32 players, was made in the wake of the 7-7 tie at the 2002 game in Milwaukee.
"The last thing you want to do is get in the situation they had a few years ago where there's a tie," said Yankees manager Joe Girardi, who will manage the American League club this July against Phillies manager Charlie Manuel's National League squad. "You don't want to get in a bind where, to me, the fans aren't seeing the best product. I like the re-entry rule and the extra player because it gives you flexibility on your roster."
Perhaps the most significant rule announced Wednesday affects those starting pitchers who are scheduled to start the Sunday before the All-Star Game, a situation that has caused much discussion the past several years.
Previously, those pitchers could be used in the game but generally would be available only for one inning, or even less, because they're only two days removed from their start. Now, a starter whose final outing before the All-Star Game falls on that Sunday will be part of the All-Star team but ineligible to pitch, and replaced on the roster.
"It makes sense," Girardi said. "If you play a game on Sunday, I know as a manager I wouldn't want that guy to pitch on Tuesday. I'd want him to maybe throw a light bullpen, but that would be it. I think that makes a lot of sense. It's unfortunate because you might see a (pitcher) deserving of the All-Star Game pitching that day, but games are important during the regular season."
Cardinals skipper Tony La Russa, who has managed five All-Star Games, is a member of the committee.
"I believe they're serious about it being a true competition, and to do that, if the game goes extra innings, you have to be able to compete," La Russa said. "You get that problem where guys are excited about being there and they don't participate, so you want to have them play. That's where the extra guy you get to protect. You always have a problem with the Sunday pitcher. No matter what they say, Tuesday is not a good day for them to pitch."
This year's squads will include 34 players, increasing the number of position players to 21 and keeping the pitching staffs at 13. Roster sizes were increased to 33 a year ago, adding the 13th pitcher spot.
One of those position players will be determined by the team's manager to be eligible to re-enter the game in the event the last position player is injured. Already, a rule is in place that allows a catcher to re-enter the game if the team's other catcher is injured.
The designated hitter rule also stipulates that the National League's DH will be chosen by the manager, while the Junior Circuit's DH will continue to be chosen by fans.
"I think it's a great idea," La Russa said. "You go through a lot of needless scorecard work if you're in the National League. Unnecessary."
John Schlegel is a reporter for MLB.com. MLB.com reporter Bailey Stephens contributed to this article. This story was not subject to the approval of Major League Baseball or its clubs.