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]