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Questions related to Major League Baseball (MLB).

The Association of Major League Baseball, often simply Major League Baseball or MLB, is the governing body that oversees the premiere professional baseball league in North America. The association, as a single legal entity, was only formed in 2000 with the official merger of the American and National Leagues, but Major League Baseball uses the formation of the Cincinnati Red Stockings (most of those players moving to the Boston Red Stockings, now the Red Sox) in 1866, as the birth of professional major-league baseball in the U.S., and thus its own history. Most historians instead point to the formation of the present-day National League in 1876 as the birth of Major League Baseball as an organization. The American League was formed in 1901, in competition with the National League, and the two leagues operated more or less independently until 1903, when an agreement establishing the two leagues as equal partners, and also establishing the World Series as the shared championship game, was signed.

The association in its current form still includes these two leagues comprising 15 teams each, 29 in the United states and one - the AL's Toronto Blue Jays - in Canada. Each league is further divided into three divisions - East, Central and West - of 5 teams each (there used to be four teams in the AL West and six in the AL East, but the Houston Astros were moved to the AL West for the 2013 season as a condition of their sale in 2012). The primary difference between these two leagues is the American League's use of the "designated hitter"; a 10th player who replaces the pitcher in the batting order but is not a defensive fielder. The National League does not allow this type of substitution; the pitcher must bat in the same inning as the one in which he pitched, or else he is considered to have been "retired" from the game and is ineligible to pitch from that point forward. When teams from the two different leagues play each other, the use of the designated hitter is based on which team is playing on their home field. The "All-Star Game" currently always uses the DH regardless of venue.

During the regular season, each team plays a schedule of 162 games, usually split into 3-game "series" (with a scattering of 2 and 4-game series) played against the same team on consecutive days. Each team will play at least 4 series against each of its division rivals, and the majority of the remaining games against other teams in the same league, though some interleague play has been scheduled for each team since 1997. Each team will play every other team in the league for at least one series during the season, and usually will face league teams in at least two series.

At the end of the regular season, the six teams that each have the overall best win-loss record in their division advance to the playoffs, as well as two "wild card" teams from each league. The two wild card teams in each league will play a single game - the Wild Card game - to determine which of them will actually advance into the playoff bracket. In the playoffs, the two pairs of teams in each league are seeded based on their overall standing, with the best team against the worst and the two middle teams against each other, and play a Divisional Series that is best-of-5 (first to win 3 games advances). The winners of those series advance to play the other league Divisional Champion in the League Championship Series, which is best-of-7 (first to win 4 games advances). The two winning teams, one from each league, win the Pennant for their league, and play the other team in a best-of-7 World Series to determine the Major League Baseball Champion.