MLB said two wild-card teams from each league will have a one-game playoff with the winner moving into the best-of-five Division Series. They would join the winners of each league's three divisions.
Enlarging the playoffs was part of the recently agreed-to collective bargaining agreement between MLB and the Major League Baseball Players Association.
"I greatly appreciate the MLBPA's cooperation in putting the new postseason format in place this year," baseball Commissioner Bud Selig said in a statement. "The enthusiasm for the 10-team structure among our clubs, fans and partners has been overwhelming.
"This change increases the rewards of a division championship and allows two additional markets to experience playoff baseball each year, all while maintaining the most exclusive postseason in professional sports."
Details on the scheduling for that one-game wild-card playoff are to be determined. The change is the first for baseball's playoff scheme since it went to eight teams in 1995.