Major League Baseball (MLB) is a professional baseball organization, the oldest of the four major professional sports leagues in the United States and Canada. A total of 30 teams now play in the National League (NL) and American League (AL), with 15 teams in each league. The NL and AL operated as separate legal entities from 1876 and 1901 respectively. After cooperating but remaining legally separate entities since 1903, the leagues merged into a single organization led by the Commissioner of Baseball in 2000.

The organization also oversees Minor League Baseball, which comprises about 240 teams affiliated with the Major League clubs. With the World Baseball Softball Confederation, MLB manages the international World Baseball Classic tournament. Baseball’s first professional team was founded in Cincinnati in 1869, 30 years after Abner Doubleday supposedly invented the game of baseball. The first few decades of professional baseball were characterized by rivalries between leagues and by players who often jumped from one team or league to another. The period before 1920 in baseball was known as the dead-ball era; players rarely hit home runs during this time. Baseball survived a conspiracy to fix the 1919 World Series, which came to be known as the Black Sox Scandal. The sport rose in popularity in the 1920s, and survived potential downturns during the Great Depression and World War II. Shortly after the war, baseball’s color barrier was broken by Jackie Robinson.