BASEBALL
MAJOR LEAGUE BASEBALL Major League Baseball ( MLB ) is a professional baseball organization, the oldest of the four major professional sports leagues in the United States and Canada . A total of 30 teams play in the National League (NL) and American League (AL), with 15 teams in each league. Baseball's first professional team was founded in Cincinnati in 1869. The first few decades of professional baseball were characterized by rivalries between leagues and by players who often jumped from one team or league to another. Today, MLB is composed of 30 teams : 29 in the United States and one in Canada. Teams play 162 games each season and five teams in each league advance to a four-round postseason tournament that culminates in the World Series , a best-of-seven championship series between the two league champions that dates to 1903.