The Everything Chess Basics Book by Peter Kurzdorfer

among captured pieces or get a hold of another set in order to make a second or third queen, for instance. If nothing is available, however, you’ll find a way.
    A New Queen
    You always have a choice as to which piece you want to turn the pawn into. But first consider the restrictions: The pawn cannot remain a pawn, and it cannot become a king. Nor can it become an enemy piece (not that you’d even want to make it into one!).
    This choice is most often not thought about at all. The queen is such a powerful piece that almost every pawn that is promoted is promoted into a queen. In fact, this is often called queening the pawn.

    White is poised to promote the pawn. Remember that White pawns move up the board, while Black pawns travel down the board.

    White has turned the little pawn into a queen. This is a rule that made it into Lewis Carroll’s Through the Looking Glass .
    Underpromotion
    Nevertheless, there are times when you might not want a queen. In these cases, it’s good to know that the choice is yours. You can promote to a rook, a bishop, or a knight, as well as a queen. As for why you might want to do such a ridiculous-seeming thing, a very simple example will suffice.

    White’s pawn is ready to promote. Should it become a queen?
    Look at the diagram. You are White and it is your move. If you promote the pawn to a queen your opponent will then checkmate you and you will lose. If, however, you underpromote the pawn to a knight, it is checkmate and you win!

    White has decided that greedily promoting to a queen and losing is not the way to go. Underpromotion to a knight produces this checkmate.
    Just keep in mind that the choice is yours every time you promote a pawn, and the choice is your opponent’s every time she promotes one of her pawns.
    Promotion with a Capture
    One of the most spectacular changes you can bring about during a chess game is to capture a piece, let’s say the opponent’s queen, with a pawn while promoting it to a queen. To gain two queens in one move is unbelievable, but it is actually possible.

    Black has a pawn for a queen. But it is Black’s move, and Black pawns march downward.

    In one move Black has transformed her pawn into a queen while capturing the White queen.
    En Passant
    Another French term in general use with chess players is en passant . This means in passing, and it refers to a particular situation that comes up from time to time in games. It doesn’t happen in more than one game in ten, perhaps, but it is a rule you should be aware of if you want to play chess or follow the games of others. To understand en passant, you have to go back to the rule about the pawn’s initial two-square option on its first move.
    The Situation

    You are playing the White pieces and have a pawn on g2. You have the option of moving that pawn to g3 or g4. Your opponent has a pawn on f4.

    But your opponent captures the pawn on g3, just as if you had moved it there!

    If you move your pawn to g3, your opponent might decide to capture your pawn with her pawn. Therefore, you decide to exercise you two-square-forward option and move your pawn to g4.
    This is perfectly legal, and it is a rule you simply have to know about. To repeat, the situation leading up to en passant is:
    • A White pawn is on the second rank, unmoved (or a Black pawn is on the seventh rank, unmoved).
    • A Black pawn is on an adjacent file on the fourth rank (or a White pawn is on an adjacent file on the fifth rank).
    • White exercises the option to move the pawn two squares forward instead of one (or Black exercises the option to move the pawn two squares forward instead of one).
    • The Black pawn that was on an adjacent file on the fourth rank captures the White pawn that has just moved two squares forward as if it had moved one square forward (or the White pawn that was on an adjacent file on the fifth rank captures the Black pawn that has just moved two squares forward as if it had moved one square forward).

    It