Minor League baseball is baseball played professionally at a level below the major leagues. It comprises both leagues and teams that are part of Organized Baseball, known by the corporate name "Minor League Baseball", and independent leagues which are not affiliated with Major League Baseball.
Minor League Baseball is the farm system for the majors. There are multiple levels of minor league baseball, ranging from Rookie Ball (limited to players in their first or second years of professional play) to Triple A, which is the step right below the major leagues. Branch Rickey, the general manager of the St. Louis Cardinals in the 1920s and 1930s, is credited with coming up with the idea after being burned by minor league operators who would sell players on option to the highest bidder. Rickey decided that if the Cardinals owned the minor league team, the Cardinals could decide the disposition of the player in question.
Originally, a minor league was a separate entity with a pennant race of its own. The clubs would try to develop talent, either by signing new players or buying players from lower levels. The team could then hold the player to win more pennants (see Lefty Grove) or sell to the majors or another minor league club to turn a profit. Now the minor leagues are part of the major league franchise itself, with six steps from Rookie to the majors. Those teams are either fully owned by the major league parent club, or are provided players and staff by the club through a working agreement which runs for a set number of years. In either case, their operations are largely subsidized by the parent club. There are sometimes a few unaffiliated teams in the minor leagues, who either independently sign players, or receive them on loan from a number of organizations.
The independent leagues operate in parallel with Organized Baseball. Their business model is more akin to what was in vogue before major league teams were roped into major league farm systems. They sign their own players and earn their profits from ticket and merchandise sales, in addition to the occasional sale of a player to a major league organization.
- Michael Clair: "How do Minor League teams pick their names? Meet the company behind the revolution", "Cut 4", mlb.com, January 26, 2017. 
- John Feinstein: Where Nobody Knows Your Name: Life In the Minor Leagues of Baseball, Doubleday, Random House, New York, NY, 2014. ISBN 978-0385535939
- Ray Giler: "Minor league baseball is better business, not bigger business", USA Today Sports, May 8, 2017. 
- George Gmelch: "Taking a Longer View of Living in the Minors", The New York Times, August 19, 2001.
- George Gmelch: Inside Pitch: Life in Professional Baseball, University of Nebraska Press, Lincoln, NE, 2006. (Originally published in 2001). ISBN 978-0-8032-7128-9
- George Gmelch and J.J. Weiner: In the Ballpark: The Working Lives of Baseball People, University of Nebraska Press, Lincoln, NE, 2006. (Originally published in 1998). ISBN 978-0-8032-7127-2
- Ernest J. Green: The Diamonds of Dixie: Travels Through the Southern Minor Leagues, Madison Books, 1995. ISBN 978-1568330433
- John Hoppin and Vicki Hoppin: Ballpark 2 Ballpark: Journey Through the Minor Leagues, 2 volumes, Black Rose Writing, Castroville, TX, 2018. ISBN 978-1-6843-3059-1
- W. Lloyd Johnson, ed.: The Minor League Register, Baseball America, Durham, NC, 1994.
- Lloyd Johnson and Miles Wolff: The Encyclopedia of Minor League Baseball, Baseball America, Durham, NC, 1997 (originally published in 1993). ISBN 0963718975
- Pat Jordan: A False Spring, University of Nebraska Press, Lincoln, NE, 2005. (originally published in 1975) ISBN 0803276265
- Jerry Klinkowitz: Owning a Piece of the Minors, Southern Illinois University Press, Carbondale, IL, 1999. ISBN 0809321947
- David Lamb: Stolen Season: A Journey Through America and Baseball's Minor Leagues, Random House, New York, NY, 1991. ISBN 039457608X
- Joseph L. Price: Perfect Pitch: The National Anthem for the National Pastime, Mercer University Press, Macon, GA, 2018. ISBN 9780881466560
- Arthur P. Solomon and Allyn I. Freeman: Making It in the Minors: A Team Owner’s Lessons in the Business of Baseball, McFarland, Jefferson, NC, 2012. ISBN 978-0-7864-6867-6
- Neil J. Sullivan: The Minors: The Struggles and the Triumph of Baseball's Poor Relation from 1876 to the Present, St. Martin's Press, New York, NY, 1990.
- David M. Sutera: Vaudeville on the Diamond: Minor League Baseball in Today's Entertainment World, Rowman & Littlelfield, Lanham, MD, 2014. ISBN 978-0810891777
- Bill Weiss and Marshall Wright: The 100 Greatest Minor League Teams of the 20th Century, Outskirts Press, Parker, CO, 2006.