“Chess960 is healthy and good for your chess. If you get into it and not just move the pieces to achieve known positions it really improves your chess vision.”
— Levon Aronian

Chess960 (also known as Fischer Random) is a chess variant where the starting position of each piece in the home rank is randomized. However, the pieces of both sides will still be symmetrical.

Rules

All the rules of standard chess apply. In particular, pieces work as if in standard chess, with the exception of castling.

Castling

Castling is legal in Chess960. Here's how it works:

1. As in standard chess, castling is not available after either the king or the castling rook has moved, or when the castling side is in check.
2. Castling can be done if there are no pieces between where the king is and the square it moves to. After castling, the king moves to where the square it would had been as in castling in standard chess. For white, they are G1 for kingside castling and C1 for queenside castling, and similar files for black.
3. The rook jumps over the king. Note that it is possible to castle even if the king does not move to a different square; however the square that the rook jumps to must be free!

In all 960 starting positions of Chess960, the pairs of rooks will always be on different sides from the king, so it is always possible to castle both kingside and queenside. Additionally, both bishops will be placed on opposite colored squares.