A glove is usually made of leather (cheaper models used mainly by children are made of synthetic materials) and is worn on the non-throwing hand. Its main features are padding to lessen the impact of the ball on the hand, and a pocket (called the crotch) between the thumb and the index finger, which allows the fielder to trap a ball with little effort and using only one hand.
There are different types of gloves worn for different positions on the field. Most particular are the gloves worn by catchers which include significantly more padding and are usually round-shaped, in order to offer a better target to the pitcher. A first baseman's glove has a very large pocket, which makes it easier to catch errant throws from infielders, but harder to dig out the ball in order to throw it to another player. Infielders, outfielders and pitchers use similar gloves, although models favored by infielders tend to be smaller, in order to make it easier to retrieve a ball from the pocket. Pitchers tend to like larger gloves, which serve no particular purpose for fielding but allow them to hide the ball better during their delivery to the plate.
Gloves are covered in Chapters 1.12 to 1.15 of the Major League Baseball Rules. The rules mention that fielders may wear gloves if they so wish, and prescribes maximum dimensions for these. The dimensions vary if the glove is for a catcher, a first baseman or another fielder. There are special requirements pertaining to the color of pitchers' gloves, in order that they not cause a distraction for the batter.
The umpire can ask a player who uses an inappropriate glove to change it, of his own initiative or when requested by a member of the opposite team.
Gloves did not exist in the earliest days of baseball. Fielders handled the ball bare-handed and the two-handed catch was the norm, as is still the case today in cricket. The development of fielding gloves in the late 19th Century introduced a new dimension to the game, by improving fielding significantly and cutting down on hand and finger injuries. The earliest gloves were very similar to leather gloves worn today to guard against the cold, but evolved into a purpose-designed piece of equipment in the early 20th Century, with the development of the pocket. While gloves were very much optional in the late 19th Century, Bid McPhee, is reputed to have been the last man to have played without using one, only starting to do so in 1896.
The first widely-manufactured and distributed glove was the Bill Doak glove, named after the St. Louis Cardinals pitcher. It was developed by Rawlings in 1920, using Doak's design for an improved pocket and proved to be an instant hit, remaining a best-seller for decades and earning Doak a sizable income. The tradition of having gloves carry the name of players has continued to this day; contrary to what one might think, the most popular models do not necessarily carry the names of the best fielders. In fact, Roger Clemens and Jose Canseco, neither of whom was known for his fielding, had their names attached to some of the most popular models of the 1990s.
Until the 1970s, gloves were often made of a very stiff type of leather and had to be broken in and seasoned before they could be used reliably in a game. This process included a number of folk recipes, such as soaking in various liquids, rubbing with oils or ointments, and wrapping the crotch around a baseball or other similarly-shaped object to form a good pocket. Modern gloves are usually made of supple leather and do not need to be broken in, although most fielders tend to favor a glove they are familiar with, as every glove has its own quirks.
Until the 1940s, it was a common practice for fielders to leave their gloves lying around their position when they left the field at the end of an inning. They would pick them up again when returning to their position after their team's turn at bat had ended. Gloves lying on the field were considered a normal obstacle, such as a pebble or the rosin bag, and a ball hitting one remained in play.
A batting glove is a glove used by a hitter to protect his hands from the sting caused by a broken bat or by a ball not hit with the thick part of the bat. It is not much different from the gloves used by golfers. In fact the first player to use such a glove was Ken Harrelson, an avid golfer, who did so in the late 1960s. Ridiculed at first, the piece of equipment quickly gained acceptance and is now used by almost every hitter.
A glove man is a player whose main or only talent is in fielding.
- Thomas Boswell: "Glove's Labor Lost", in How Life Imitates the World Series, Penguin Books, New York, NY, 1982, pp. 134-136.
- Brian Murphy: "Babe Ruth glove auctioned for record $1.53 million", mlb.com, November 12, 2022. 
- Chuck Rosciam: "The Evolution of Catcher's Equipment", in The Baseball Research Journal, SABR, Volume 39, Number 1 (Summer 2010), pp. 104-112.
- Steve Steinberg: "William Leopold Doak", in Tom Simon, ed.: Deadball Stars of the National League, SABR, Brassey's Inc., Dulles, VA, 2004, pp. 358-360.