Major League Baseball (MLB) is a professional baseball organization, which consists of a total of 30 teams—15 teams in the National League (NL) and 15 in the American League (AL). The NL and AL were formed in 1876 and 1901, respectively. Beginning in 1903, the two leagues cooperated but remained legally separate entities until 2000 when they merged into a single organization led by the Commissioner of Baseball. This list documents all 30 active MLB teams ranked by win–loss percentage as of the completion of the 2021 Major League Baseball season. These records do not include results from by a team's playing time in the National Association of Professional Base Ball Players or while members of any minor league.