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Minor League Baseball (MiLB) is professional baseball below Major League Baseball (MLB), including teams affiliated with MLB clubs and independent baseball leagues consisting of unaffiliated teams.
Entering the 2021 season, the number of full-season MLB-affiliated minor leagues with teams in the United States and Canada was reduced to 11, with a total of 120 teams (four per each of the 30 MLB franchises). There are also two affiliated rookie leagues based in the United States, with teams based at the parent clubs' spring training complexes in Arizona and Florida, and one affiliated rookie league in the Dominican Republic.
Organization
As of the 2022 season, the minor league system is divided into four classes: Triple-A (AAA), Double-A (AA), High-A (A+), and Single-A (A).[a] MLB franchises may also maintain one or two complex-based rookie teams in the Arizona Complex League or Florida Complex League, and international summer baseball teams in the Dominican Summer League. While major league teams play a 162-game schedule, minor league seasons are shorter. As of 2022, a complete season in Triple-A is 150 games, Double-A is 138 games, and High-A and Single-A are each 132 games.
Triple-A
This classification currently includes two affiliated leagues: the 20-team International League and the 10-team Pacific Coast League (known as Triple-A East and Triple-A West, respectively, for the 2021 season). For most of the 20th century, Triple-A also included the American Association, based in the Midwest, but that league disbanded with its clubs absorbed by the other two leagues, as part of a reorganization of the Triple-A level in 1997. The International League features teams from the Atlantic coast and midwestern U.S., while the Pacific Coast League features teams from the Pacific coast and the southwest.
Both young players and veterans play for Triple-A teams. Parent clubs often hold players who are on the 40-man roster, but not on the active MLB roster, at the Triple-A level. Such players are eligible to be added to a team's active major league roster. For teams in contention for a pennant late in a season, it gives them fresh players, while for teams not in contention, it gives them an opportunity to evaluate their second-tier players against major league competition. Some Triple-A players are "career minor leaguers", former prospects whose skill growth has halted and who are not likely to advance to MLB, unless as a temporary replacement.
Double-A
There are currently three leagues in this classification: the 12-team Eastern League (known as Double-A Northeast for the 2021 season), with teams in the Northeast and Mid-Atlantic regions of the U.S., the 8-team Southern League (known as Double-A South for the 2021 season), with teams in the Deep South, and the 10-team Texas League (known as Double-A Central for the 2021 season), with teams in the Southwest and Great Plains.
Some players jump to the majors from this level, as many of the top prospects are put here to play against each other rather than against minor and major league veterans in Triple-A. A small handful of players might be placed here to start, usually veterans from foreign leagues with more experience in professional baseball. The expectation is usually that these veteran players will be in the majors by the end of the season, as their salaries tend to be higher than those of most prospects.
High-A
One level below Double-A is the High-A level, named "Class A-Advanced" before 2021. This classification has three leagues: the 12-team Midwest League (known as High-A Central for the 2021 season), covering the Midwest, the 6-team Northwest League (known as High-A West for the 2021 season), with teams in the Pacific Northwest, and the 12-team South Atlantic League (known as High-A East for the 2021 season), with teams in the eastern states. All three leagues were reclassified prior to the 2021 season, with the Midwest League and the South Atlantic League promoted from Single-A and the Northwest League promoted from Class A Short Season.[9]
This level of play is often a second or third promotion for a minor league player, although a few high first-round draftees, particularly those with college experience, begin at this level.
Single-A
Below the High-A level is Single-A, named "Class A" before 2021, when it was also known as Single-A or Full-Season A,[b] and "Low-A" for the 2021 season. This classification has three leagues: the 8-team California League (known as Low-A West for the 2021 season), located entirely in California, the 12-team Carolina League (known as Low-A East for the 2021 season), and the 10-team Florida State League (known as Low-A Southeast for the 2021 season). All three leagues were demoted from High-A to Single-A effective with the 2021 season.
These leagues are a mix of players moving up from Rookie leagues, as well as the occasional experienced first-year player. Most of the teams in the Florida State League are owned by major league parent clubs and use their spring training complexes.
In 2022, the official name of the class became Single-A.
Rookie
Minor leagues with the Rookie classification play a shortened season, starting in mid-June and ending in late August or early September. This lowest level of minor league baseball consists of two US-based leagues, the Arizona Complex League and Florida Complex League (known as the Arizona League and Gulf Coast League, respectively, before 2021), and one Caribbean-based league, the Dominican Summer League.
The US-based Rookie leagues play a schedule of approximately 60 games and are named "complex leagues" because games are played at their parent clubs' spring training complexes. Rosters consist primarily of newly drafted players who are not yet ready for a higher level of play. These leagues are intended almost exclusively to allow players to hone their skills; no admission is charged and no concessions are sold.