Chess Strategies, Hints, and Tips – When is it legal to castle?

Delores Keeper
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Hey. As this is a new blog, I figure I’ll start with the most basic questions about the rules of chess and then later we’ll get into some killer strategies. When I started playing chess there were two arguments that occurred over and over; when can you castle, and how does en passant work? This week we’ll answer the question of castling.

You can castle when:
1) Neither the king nor the rook involved have moved at any time previously,
2) All of the squares between the king and rook are clear,
3) The king is not in check, the square(s) the king will pass through are not threatened, and the square the king will end up on is not threatened.

In other words you CAN castle when the rook is threatened. You can castle queenside when the square next to the rook is threatened (b1 for the white player, b8 for black) but none of the squares the king would pass through are threatened. I love the diagram below that I saw on a FAQ about castling:

This would be a situation where it was legal to castle queenside if neither the king nor rook had moved previously in the game (of course you would be in checkmate the next move, but that’s just details). The rook is threatened, the square next to the rook is threatened, but the king is not threatened nor are any of the squares the king will pass through.