Major League Baseball (MLB) is a professional baseball organization that constitutes one of the four major professional sports leagues in North America. MLB teams play in the American League (AL) and National League (NL), which operated as separate legal entities from 1901 and 1876 respectively. In 2000, the leagues merged into a single organization led by the Commissioner of Baseball. The organization oversees minor league baseball leagues, which operate about 240 teams affiliated with the major-league clubs. With the International Baseball Federation, the league also manages the international World Baseball Classic tournament.