Feeder system for major league baseball in the United States and Canada. Different levels or "classes" of leagues exist, similar to the division structure in FIFA-endorsed soccer leagues worldwide; unlike those systems, no promotion/relegation exists in minor league baseball (or in any other North American professional sport, for that matter). This is because (a) most teams are semi-permanently affiliated with one particular major league club, which supplies players, pays their salaries and moves them up and down the ladder as necessary, and (b) the differences in stadium size and TV market size are much more pronounced between the majors and AAA ball (imagine, say, the Chicago White Sox and Chicago Cubs being relegated in favor of the Rochester Red Wings and Fresno Grizzlies) than in most international soccer systems.

Listed below are all leagues containing major league-affiliated clubs. In addition, the AAA-level Mexican League is also governed by the National Association of Professional Baseball Leagues, the minors' governing body, but operates mostly on its own; several independent leagues (not part of the National Association) also exist, with varying levels of play.

Classes and leagues: