Castling, en passant and promotion

Three moves break the ordinary rules, and all three decide games. Castling moves two pieces at once and tucks your king away; it has five conditions and beginners forget at least two of them. En passant lets a pawn capture a pawn that tried to sneak past it, and it is legal for exactly one move. Promotion turns a pawn that reaches the far rank into a queen, or into a knight when a queen would be stalemate. I have watched adults lose a rook to en passant and then argue it was not a real rule. It is. Every page here gives the rule, the conditions, the one exception people miss, and a board you can check it on.

1. What is castling in chess?

   Castling is the one move that shifts two pieces at once.

2. Castling rules: the five conditions

   You may castle only if your king has never moved, the rook you are castling with has never moved, every square between them is empty, your king is not in check, and neither the square it crosses nor the square it lands on is attacked.

3. When can you not castle?

   You cannot castle when your king has already moved, when the rook on that side has already moved, when any piece stands between them, when you are in check, or when the king would cross or land on a square an enemy piece attacks.

4. Can you castle out of check?

   No.

5. Can you castle through check?

   No.

6. Can you castle after moving the king?

   No.

7. Can you castle after the rook has moved?

   Not with that rook, ever again, even if it goes back to the corner.

8. Can you castle queenside?

   Yes, and it is written O-O-O.

9. Kingside vs queenside castling

   Kingside (O-O) is two squares to clear and puts the king in the corner behind an untouched f2, g2, h2.

10. Is castling one move?

    Yes.

11. Which piece do you move first when castling?

    The king.

12. What is en passant in chess?

    En passant is a pawn capture.

13. En passant rules: when it is allowed

    Four conditions have to hold: your pawn is on its fifth rank, an enemy pawn on the file next door moves two squares in one go from its starting rank, it lands directly beside your pawn, and you capture on your very next move.

14. Why does en passant exist?

    Pawns originally moved one square at a time.

15. Is en passant mandatory?

    No.

16. Can any piece capture en passant?

    No.

17. What is pawn promotion?

    When a pawn reaches the last rank, the eighth for White and the first for Black, it is exchanged as part of the same move for a new queen, rook, bishop or knight of its own colour.

18. What can a pawn promote to?

    A queen, a rook, a bishop or a knight, always of your own colour.

19. Can you have two queens in chess?

    Yes.

20. Do you have to promote to a queen?

    No.

21. Can a pawn promote to a king?

    No.

22. How to promote when you have no spare queen

    Stop the clock and ask the arbiter for a queen: the Laws allow you to stop the clock for exactly that kind of help.