Throughout the season, during the Interleague, teams will play against designated teams from a different division for the year.
From 1997 through 2001, teams competed against each other in the same Division, but in 2002, Interleague games were played. The East Division of American League played against teams from the West Division of National League, the Central Division of American League, the East Division of National League, and so on.
Every year, the Major League office decides and announces the schedule of Interleague play.
During Interleague games, each team plays around 20 games. If two teams are from the same division, they will play six games with a team from the same division.
(Ex: New York Yankees and New York Mets, Chicago Whites and Chicago Cubs, and LA Angels and LA Dodgers.)