There are 14 Minor League Baseball (MiLB) leagues and 206 teams in operation across the United States, Dominican Republic, and Canada, which are affiliated with Major League Baseball (MLB) teams. They are organized by one of five classes (from highest to lowest): Triple-A, Double-A, High-A, Single-A, and Rookie. Of these, 120 teams in 11 leagues (from Triple-A to Single-A) are each affiliated with one MLB team through a standardized professional development license. Additionally, three leagues consisting of a total of 85 Rookie teams are located at MLB spring training complexes in Arizona and Florida, as well as in the Dominican Republic.[1] These affiliated leagues contest their seasons during the MLB season.
The Arizona Fall League, consisting of six teams, operates in the autumn after the conclusion of the MiLB and MLB seasons to develop top prospects at various classifications.
Seven independent baseball leagues, consisting of a total of 69 teams, have no direct affiliation with Major League Baseball, though the American Association, Atlantic League, Frontier League, and Pioneer League are designated MLB Partner Leagues.[2]
The Triple-A classification is the highest level of play in Minor League Baseball, just below Major League Baseball. A total of 30 affiliated teams compete at this level, with 20 teams in the International League and 10 teams in the Pacific Coast League.[3]
The Double-A classification is the second-highest level of play in Minor League Baseball. A total of 30 teams compete at this level, with 12 teams in the Eastern League, 8 teams in the Southern League, and 10 teams in the Texas League.[3]
High-A is the third-highest level of play in Minor League Baseball. A total of 30 teams compete at this level, with 12 teams in the Midwest League, 12 teams in the South Atlantic League, and 6 teams in the Northwest League.[3]
Single-A is the fourth-highest level of play in Minor League Baseball. A total of 30 teams compete at this level, with 12 teams in the Carolina League, 10 teams in the Florida State League, and 8 teams in the California League.[3]
The Rookie classification is the lowest level of play in Minor League Baseball. A total of 85 teams compete at this level, with 18 teams in the Arizona Complex League,[4] 20 teams in the Florida Complex League,[5] and 47 teams in the Dominican Summer League.[6]
The Arizona Fall League, an off-season league owned and operated by Major League Baseball, consists of six teams in the state of Arizona.[7]
MLB Partner Leagues consist of 50 teams with no direct affiliation with individual MLB organizations, but collaborate on promoting the sport in North America. Three leagues—the American Association, Atlantic League, and Frontier League, had been fully independent leagues—while the Pioneer League had previously been a Rookie-classification affiliated league.
The American Association of Professional Baseball consists of 12 teams.[8]
The Atlantic League of Professional Baseball consists of 10 teams.[9]
The Frontier League consists of 16 teams.[10]
The Pioneer League consists of 12 teams.
The independent Empire Professional Baseball League consists of 4 teams.[11]
The independent Pecos League consists of 16 teams.[12]
The independent, single-site United Shore Professional Baseball League consists of four teams.[13]
