Major League Baseball (MLB) is the highest level of play in North American professional baseball. Specifically, Major League Baseball refers to the organization that operates the National League and the American League, by means of a joint organizational structure that has developed gradually between them since 1901 (the National League having been in existence since 1876). In 2000, the two leagues were officially disbanded as separate legal entities with all their rights and functions consolidated in the commissioner's office.[4] MLB effectively operates as a single league and as such it constitutes one of the major professional sports leagues of the United States. It is currently composed of 30 teams—29 in the United States and one in Canada. In conjunction with the International Baseball Federation, the MLB also manages the World Baseball Classic.