The Manager is the person responsible for the day-to-day running of a baseball team, and especially for taking in-game decisions. These days, the manager tends to be a former player who reports to the General Manager, who is in turn responsible for acquiring and getting rid of players. In baseball's early days, the manager tended to be a field captain, that is one of the players tasked with the responsibility of making tactical decisions during a game. This role evolved into that of player/manager, which was quite common until World War II. The last player/manager in Major League Baseball was Pete Rose, who managed the Cincinnati Reds while still an active player from 1984 to 1986. Baseball managers are distinguished from their counterparts in other sports because they normally wear the team's uniform and not civilian clothes. A manager who does not wear a uniform is confined to the dugout during the game, and may not go onto the field to give his players instructions or talk to an umpire.
The manager's tasks include both human resource management and tactical management. In the first category, he is responsible for maintaining harmony in the clubhouse, applying discipline when needed, and defining the role that each of his players fills on the team. With the assistance of coaches, he is also a teacher of baseball skills and a fixer of technical flaws among his players. He is also expected to stand up for his players, both by acting as a spokesman for the team with the media, and by arguing on their behalf when they are the victims of unfavorable or erroneous decisions by an umpire.
The manager's tactical duties include longer-term functions such as determining who are the regulars and who are the substitutes and at which positions, and how much playing time should each player get. Shorter-term responsibilities include deciding on the starting line-up, including naming the starting pitcher, ordering substitutions, and in-game tactical moves such as calling for the hit-and-run, the sacrifice bunt or the stolen base, and deciding on when to use relievers, pinch hitters, pinch runners and defensive substitutes.
It is rare that a manager excels at all these various aspects of the job. Fans tend to concentrate on the most immediate issues of in-game tactics to judge the value of a manager, while front office personnel will look more at longer-term issues of clubhouse harmony, player development and ability to implement an organizational plan or philosophy.
In his essay "From Little Napoleons to Tall Tacticians", Thomas Boswell identifies four main personality types among baseball managers, corresponding to archetypes based on the nicknames of their earliest representatives in Major League Baseball, all of whom are in the Hall of Fame:
- The Little Napoleons, modeled on John McGraw, intense, emotional and competitive, embodying passionate leadership.
- The Peerless Leaders, modeled on Frank Chance, disciplined, courageous and dignified, embodying leadership by character.
- The Tall Tacticians, after Connie Mack, savvy, intelligent and trusting in their judgment, embodying intellectual leadership; and
- The Uncle Robbies, after Wilbert Robinson, compassionate, humorous and understanding, embodying leadership by wisdom.
- Thomas Boswell: "From Little Napoleons to Tall Tacticians", in Why Time Begins on Opening Day, Penguin Books, New York, NY, 1984, pp. 83-103.
- Thomas W. Brucato: Baseball Skippers and Their Crews: The History of Every Major League Manager and Coach, 1871-2007, St. Johann Press, Haworth, NJ, 2008. ISBN 978-1-878282-50-7
- Donald Honig: The Man in the Dugout: Fifteen Big League Managers Speak Their Minds, University of Nebraska Press, Lincoln NE, 1995. (oriinally published in 1977) ISBN 0803272707
- Chris Jaffe: Evaluating Baseball's Managers: A History and Analysis of Performance in the Major Leagues, 1876-2008, McFarland, Jefferson, NC, 2010.
- Bill James: The Bill James Guide to Baseball Managers from 1870 to Today, Scribner Books, New York, 1997. The book includes both a history of Managers and a study of managing in baseball, including the concept of different levels of decision-making.
- Harold Kaese: "No Pattern for Managers", Baseball Digest, May 1948, pp. 73-74. 
- John C. Skipper: A Biographical Dictionary of Major League Baseball Managers, McFarland, Jefferson, NC, 2003.
- Gary Webster: When in Doubt, Fire the Skipper: Midseason Managerial Changes in Major League Baseball McFarland, Jefferson, NC, 2013. ISBN 978-0-7864-7892-7