Major League Baseball has a first-year player draft every June. Each team drafts 50 college and high school players into their organization. Additionally, foreign players sign as free agents. Players are assigned to a minor league team with the ultimate goal of reaching the major leagues. First, they must climb the minor league ladder. As of 2010, there were six levels of minor league baseball spread among 20 leagues and more than 251 teams.
The minor leagues begin with the six Rookie Leagues, which start shortly after the June draft. The new draft picks play a 56- to 76-game schedule, depending on the league. Teams can't use players that have more than three years of previous minor league experience. The Rookie Leagues include the Appalachian League, the Arizona Summer League, the Gulf Coast League and the Pioneer League. Additionally, the Dominican Summer League and the Venezuelan Summer League use only foreign players–American and Canadian players aren’t allowed.
Class A-Short Season
The Class A-short season leagues consist of the New York Penn League and the Northwest League. The teams also begin their season in June with recent draft picks. Teams can also use three players on their 30-member active list that have played four or more years in minor league baseball. Also, a pitcher switching to a fielding position–and a position player becoming a pitcher–can play one Class A-short season regardless of the amount of previous experience. The teams play 76-game schedules.
The Class A level gives minor leaguers their first taste of the rigors of playing every day over an extended season. The Midwest League and the South Atlantic League play a 140-game schedule from April to early September. A player often earns his first promotion to this level.
The Class A-advanced level consists of the California League, the Carolina League and the Florida State League. The season is similar to the Class A schedule, with 140 games from April to September. But as the name indicates, the quality of play is better than the two other Class A levels. Players who excel in those leagues get promoted to Class A-advanced.
Major league teams often promote Double-A players straight to the big leagues, while bypassing Triple-A. The level consists of the Eastern League, the Southern League and Texas League. Their rosters contain many of the game’s top prospects. Teams play a 140-game schedule from April to September.
Triple-A is the sixth and final level of minor league baseball. The International League, the Mexican League and the Pacific Coast League all field teams that play approximately 145 games. The rosters feature a mix of players promoted from Double-A, former major leaguers trying to restart their career and major league players recovering from an injury or demoted from the parent club. Struggling players get to work on problem areas with hope of getting recalled to the majors. It also has tweeners--players whose skill level is better than Triple-A, but not quite good enough for the majors.