MLB has got two leagues, each with three divisions of five teams. The current league structure has been unchanged since 2013 when the Houston Astros team moved from the National League to the American League. In 1998, Milwaukee Brewers moved from AL to NL. Within each of the leagues there were more transfers to another city.

The World Series is the final of the playoffs in which the American League and National League playoff winners compete.

Until 2002, the home advantage of the first World Series match alternated between AL and NL, from 2002 to 2016, the home team won the star team's victory. Since 2017, the home environment has a team with better results in the basic part.