Major League Baseball (MLB) is a professional baseball organization that is the oldest of the four major professional sports leagues in the United States and Canada. A total of 30 teams now play in the American League (AL) and National League (NL), with 15 teams in each league. The AL and NL operated as separate legal entities from 1901 and 1876 respectively. After cooperating but remaining legally separate entities since 1903, in 2000 the leagues merged into a single organization led by the Commissioner of Baseball. The organization also oversees minor league baseball leagues, which comprise about 240 teams affiliated with the major-league clubs. With the World Baseball Softball Confederation, MLB manages the international World Baseball Classic tournament.