What are the FIDE Laws of Chess?
The whole official rulebook of chess is one short document, and two of its articles cause almost every argument at a club.
FIDE is the world chess federation. It publishes that document, called the Laws of Chess, and every official tournament in the world plays by it.
The Laws are short. They say how the board is set up, how each piece moves, how a game ends, and what an arbiter does when something goes wrong. An arbiter is the referee of a chess tournament.
The Laws are numbered by article. When a rule is quoted on this page, the article number is given so you can look it up. The two troublesome articles are article 4, which is the touch-move rule, and article 7.5, which is the illegal move rule.
What are the FIDE rules for castling?
Castling moves your king two squares towards a rook, and that rook jumps to the square the king crossed. Article 3.8 of the Laws covers it.
Castling on the king side is written O-O. Castling on the queen side is written O-O-O.
You may castle only when all six of these are true:
1. Your king has not moved yet in this game.
2. That rook has not moved yet in this game.
3. Every square between the king and that rook is empty.
4. Your king is not in check right now.
5. The square your king crosses is not attacked by an enemy piece.
6. The square your king lands on is not attacked by an enemy piece.
Two things people get wrong. First, an attacked rook does not stop castling; only the king's squares matter. Second, once your king has moved, you can never castle again, even if you move it straight back.
What is en passant?
En passant is a pawn capture with one condition attached. Article 3.7 of the Laws describes it.
It happens like this. Your pawn stands on the fifth row from your side. An enemy pawn beside it pushes two squares in one go, landing next to your pawn. On your very next move you may capture it as if it had moved only one square.
The captured pawn is taken off the board even though your pawn never landed on its square. That surprises people the first time they see it.
You lose the right the moment you play any other move. There is no way to claim it later.
When does a pawn promote, and what can it become?
A pawn that reaches the far end of the board must change into another piece at once. This is called promotion.
You choose a queen, a rook, a bishop or a knight of your own colour. You cannot stay a pawn and you cannot become a king.
You may choose a piece you already have. Two queens on the board is normal and completely legal.
Almost every promotion should be a queen. Now and then a knight is better, because a knight can give check on squares a queen cannot reach. Choosing a piece other than the queen is called underpromotion.
What is the difference between check, checkmate and stalemate?
Check means your king is attacked. You must get out of it on this move. You can move the king away, block the attack, or capture the attacking piece. Any move that leaves your own king attacked is illegal.
Checkmate means your king is attacked and nothing gets it out. The game ends at once and the attacker wins.
Stalemate means it is your turn, your king is not attacked, and you have no legal move at all. The game is a draw. Article 5.2.1 says so.
This catches out beginners with a big lead. If you take away every one of your opponent's moves without giving check, you have thrown away the win.
What happens if you make an illegal move?
An illegal move is any move the Laws do not allow. Leaving your own king in check is the most common one.
Article 7.5 says the move is taken back and the position is put back as it was. Then the penalty is applied.
In a standard-length game your first completed illegal move gives your opponent two extra minutes on the clock. Your second illegal move in the same game loses the game.
Since 2018 rapid and blitz work the same way. Two other things count as illegal moves under article 7.5. Pressing your clock without having made a move is one. Using two hands to make a single move is the other.
What is the touch-move rule?
Article 4.3 says that if you touch one of your own pieces, you must move it if it has a legal move. If you touch an enemy piece, you must capture it if you can capture it legally.
If you want to straighten a piece on its square, say "j'adoube" first. It is French for "I adjust". Say it before you touch the piece, never after.
Article 4.4 covers castling. If you touch your king and a rook at the same time, you have said you want to castle. Article 4.7 says that once you let go of the king on its new square, the castling is done.
What do the Laws say about the clock?
In a tournament each player has their own clock. You make your move, then you press your clock, which starts your opponent's.
Article 6.2.3 says you must press the clock with the same hand you moved with. Moving with one hand and pressing with the other is not allowed.
If your time runs out you lose, with one exception. If your opponent has so little material that no series of legal moves could ever checkmate you, the game is a draw instead.
You are also expected to write the moves down yourself in a standard-length game. Nobody writes them down for you.