Major League Baseball (MLB) is the highest level of play in North American professional baseball. More specifically, Major League Baseball refers to the organization that operates North American baseball's two major leagues, the National League an the American League, by means of a joint organizational structure that has existed between them since 1903. Major League Baseball teams play a 162-game season, which generally begins on the first Sunday in April and ends on the first Sunday in October, with playoffs played in October and early November. The two leagues follow the same rules, with one exception: the American League operates under the Designated Hitter Rule, while the National League does not. Utilization of the DH Rule in Interleague, All-Star and World Series games is determined by the home team's league rules. In 2000, the American and National Leagues were officially disbanded as separate legal entities with all rights and functions consolidated in the commissioner's office. MLB effectively operates as a single league and as such it constitutes one of the major professional sports leagues of North America.