En Passant Explained

En passant — French for 'in passing' — is the single rule in chess that surprises new players more than any other, because it looks like an exception being invented on the spot the first time you see it. It isn't; it's a completely standard, always-legal rule, just one that only applies in a narrow, specific situation.

The situation it applies to

Remember that a pawn is allowed to move two squares on its very first move. En passant exists specifically to handle what happens when that two-square jump would otherwise let a pawn slide past an enemy pawn that could have captured it if it had only moved one square at a time.

How the capture actually works

If an enemy pawn uses its two-square first move to land directly beside your pawn (on the same rank, one file over), you may capture it as though it had only moved one square — removing it from the board and moving your own pawn diagonally onto the square it passed over, exactly like a normal pawn capture. The captured pawn ends up gone even though your pawn technically lands behind where the enemy pawn actually is.

Why the rule exists at all

Without en passant, the two-square first move would create a strange loophole: a pawn could always safely dash past an enemy pawn sitting right next to it, using the double-step specifically to avoid a capture that would have been possible with a normal single-square advance. En passant closes that loophole by treating the double-step, for capturing purposes only, as if it were a normal one-square move.

Recognizing it on this site's boards

When you see a move labeled with an 'x' immediately after what looks like a pawn simply advancing into empty space next to another pawn, that's en passant in action — the captured pawn isn't sitting on the square being moved to, which is exactly what makes this capture look unusual the first few times you see it.

It's more common than you'd think

Because pawns advance to their starting battle lines constantly in the opening moves of a game, opportunities for en passant come up in a real fraction of games, not just in rare puzzle positions. It's genuinely worth checking for on every move where an opponent's pawn has just made a two-square advance next to one of yours.

For a refresher on how captures are written in general, see chess notation explained — en passant captures are written exactly like any other pawn capture, with nothing special added to flag it.