The pawn (♙♟) is the weakest and most numerous piece in the game of chess, representing infantry, or more particularly armed peasants or pikemen. Each player begins the game with eight pawns, one on each square of the second rank from the view of the player. In algebraic notation the white pawns start on a2, b2, c2, ..., h2, while the black pawns start on a7, b7, c7, ..., h7.
Pawns are differentiated by the files on which they currently stand. For example, one speaks of "White's f-pawn" or "Black's b-pawn"or, less commonly, "White's king's bishop's pawn" or "Black's queen's knight's pawn" (using descriptive notation). It is also common to refer to a rook pawn, meaning any pawn on the a-file or h-file, a knight pawn (on the b- or g-file), a bishop pawn (on the c- or f-file), a queens pawn (on the d-file), a kings pawn (on the e-file), and a central pawn (on either the d- or e-file).
As pawns differ so much from other pieces, the usage of the word pieces in chess literature usually excludes the pawns, although this distinction between "pieces" and "pawns" is not found in the official rules.
The choice of promotion is not limited to captured pieces. It is both legal and possible for one player to simultaneously have as many as ten knights, ten bishops, ten rooks or nine queens. While this extreme would almost never occur in practice, in game 11 of their 1927 world championship match, José Raúl Capablanca and Alexander Alekhine each had two queens in play at once. While some finer sets do include an extra queen of each color, most standard chess sets do not come with additional pieces, so the physical piece used to replace a promoted pawn is usually one that was previously captured. When the correct piece is not available, some substitute is used: a second queen is often indicated by inverting a previously captured rook or a piece is borrowed from a different set. This issue does not arise in computer chess.
Promotion is often called "queening", because the piece chosen is nearly always a queen. When some other piece is chosen it is known as "underpromotion" and the piece selected is most often a knight used to execute a checkmate or a fork giving the player a net increase in material compared to promoting to a queen. Underpromotion is also used in situations where promoting to a queen would give instant stalemate and the promotion cannot be deferred until this situation has ceased.
Here, White has a long-term space advantage. White will have an easier time than Black in finding good spaces for friendly pieces, particularly with an eye to the kingside. Black, in contrast, suffers from a bad bishop on c8, which is prevented by the black pawns from finding a good square or helping out on the kingside. On the other hand, White's central pawns are somewhat over-extended and vulnerable to attack. Black can undermine the white pawn chain with an immediate c7-c5 and perhaps a later f7-f6.
Pawns on adjacent files can support each other in attack and defense. A pawn which has no friendly pawns in adjacent files is an isolated pawn. The square in front of an isolated pawn may become an enduring weakness. Any piece placed directly in front not only blocks the advance of that pawn, but cannot be driven away by other pawns.
In the diagram at right, Black has an isolated pawn on d5. If all the pieces except the kings and pawns were removed, the weakness of d4 might prove fatal to Black in the endgame. In the middlegame, however, Black has slightly more freedom of movement than White, and may be able to trade off the isolated pawn before an endgame ensues.
A pawn which cannot be blocked or captured by enemy pawns in its advance to promotion is a passed pawn. In the diagram at left, White has a passed pawn on a4. Black's pawn on g7 is not a passed pawn, because it has to get by White's h2 pawn before it can be promoted. Because endgames are almost always won by the player who can promote a pawn first, having a passed pawn in an endgame can be decisive. In this vein, a pawn majority, a greater number of pawns belonging to one player on one side of the chessboard, is strategically important because it can be converted into a passed pawn.
The diagrammed position might appear roughly equal, because each side has a king and five pawns, and the positions of the kings are about equal. In truth, White should win this endgame on the strength of the passed pawn, no matter who makes the first move.
After a capture with a pawn, a player may end up with two pawns on the same file, called doubled pawns. Doubled pawns are substantially weaker than pawns which are side by side, because they cannot defend each other, and the front pawn blocks the advance of the back one. In the diagram at right, Black is playing at a strategic disadvantage due to the doubled c-pawns.
There are situations where doubled pawns confer some advantage, typically when the guarding of consecutive squares in a file by the pawns prevent an invasion by the opponent's pieces.
Pawns which are both doubled and isolated are typically a tangible weakness. A single piece or pawn in front of doubled isolated pawns blocks both of them, and cannot be easily dislodged. It is rare for a player to have three pawns in a file, i.e. tripled pawns. Depending on the position, tripled pawns may be more or less valuable than two pawns which are side by side.
In medieval chess, an attempt was made to make the pieces more interesting, each rank's pawn being given the name of a commoner's occupation, from left to right:
The most famous example of this is the second book ever printed in English, The Game and Playe of the Chess, which indeed was seen as much as a political commentary on society as a chess book, and was printed second by William Caxton because it was, like the Bible, among the most popular books of its day.
The ability to move two spaces, and the resulting ability to have an en passant capture, were only introduced in 15th century Europe. The rule for promotion has changed through history, see promotion (chess)#History of the rule.
Because the pawn is the weakest piece, it is often used metaphorically to indicate unimportance or outright disposability, for example, "I'm only a pawn in the game of life."
In most other languages, the word for pawn is similarly derived from paon or some other word for foot soldier. Exceptions are, for example, the Irish fichillín, which means "little chess", and the German "Bauer", which means farmer.