En Passant, Explained: The Chess Rule Everyone Forgets

En passant — French for "in passing" — is the rule new players most often either forget exists or misuse once they remember it. It lets a pawn capture an enemy pawn that has just moved two squares, as though it had only moved one, and it is legal only on the very next move.

The situation: a pawn sits on its fifth rank (White's pawn on the fifth rank, Black's on the fourth). An enemy pawn on an adjacent file pushes two squares in one move, landing beside it rather than in front of it — which means it slipped past the square where it could normally have been captured. En passant restores that capture. The attacking pawn takes the enemy pawn as if it had stopped on the skipped square, and moves there itself.

The rule exists because of a change made centuries ago, not from the beginning of chess. Originally every pawn moved one square at a time. The two-square first move was added later to speed the opening up, and it created a loophole: a pawn could now dash straight past an enemy pawn poised to capture it, entirely avoiding a fight it would otherwise have had to have. En passant closes that loophole, so the two-square move cannot be used to sneak past a waiting pawn.

Three conditions all have to hold, and missing any one of them is the usual source of confusion. The capturing pawn must already be on its fifth rank. The captured pawn must have just moved two squares from its starting position — a pawn that moved two squares several moves ago, or one that started from a square it was pushed to earlier, does not qualify. And the capture must be made immediately, on the very next move; wait one move and the right to capture en passant is gone for good, even though the pawns are still sitting right next to each other.

That last condition is where almost every mistake happens. A player notices the possibility two or three moves later, tries to play it, and finds their chess app or opponent correctly refuses it. The right has already expired. If you think en passant might be available, check for it before you play anything else that turn, because it is the one capture in chess with an expiry date measured in a single move.

It is also entirely optional. Nothing forces the capture; the pawn is free to stay put and the enemy pawn is free to sit there unmolested. And it can only ever be played by a pawn capturing a pawn — it has nothing to do with any other piece, despite occasionally being confused with castling as "another one of the weird special rules."

The reason it is worth actually knowing rather than half-remembering is tactical, not just administrative: missing that an en passant capture is available can cost real material in a sharp position, and missing that your opponent has one available against you is an easy way to lose a pawn, or open a file, without any warning. It looks obscure the first time you see it and becomes completely automatic within a few games once you know the three conditions.