En passant

The en passant capture — French for “in passing” — is the only chess rule that lets a piece capture an enemy piece on a square the enemy piece never landed on. It exists for a single structural reason: when the two-square initial pawn advance was added to the rules in the fifteenth century, it created a problem where a pawn could rush past an enemy pawn that should, by the older rules, have been entitled to capture it. En passant restores the symmetry. A pawn that has just moved two squares can be captured by an enemy pawn on the adjacent file, exactly as though it had moved only one square.

How the capture works

The rule applies in one specific situation. After your opponent advances a pawn two squares from its starting rank — a white pawn from the second rank to the fourth, or a black pawn from the seventh to the fifth — and the advancing pawn lands on a square adjacent to one of your own pawns on the same rank, you may, on your immediately following move, capture the advancing pawn as if it had only advanced one square. Your pawn moves diagonally to the square the advancing pawn passed over, and the advanced pawn is removed from the board.

A concrete example: White plays a pawn from e2 to e4. Black has a pawn on d4 or f4. On Black’s next move, Black may play d4xe3 or f4xe3 — capturing the white pawn that is on e4, as if it were on e3.

The strict timing requirement

The capture must be made on the move immediately following the two-square advance. If you do not capture, you lose the right to do so for that pawn forever. The right does not persist; it is a single-move window.

This is the single most-misunderstood part of the rule. Players who first learn en passant often assume the right persists as long as the two pawns remain adjacent. It does not. The right exists for exactly one move, and disappears if not exercised on that move.

When the capture is and is not available

En passant is only available when:

The capturing piece is a pawn. Other pieces — knights, bishops, queens, kings — cannot capture en passant.

The captured piece is also a pawn. En passant does not apply to any piece other than a pawn.

The captured pawn has just advanced two squares. A pawn that has advanced two squares earlier (then sat on the fourth or fifth rank for several moves) cannot be captured by en passant.

The capturing pawn was on the fifth rank (for White) or the fourth rank (for Black) — that is, on the rank adjacent to the captured pawn’s destination square after its two-square move.

The capturing pawn was on the file adjacent to the captured pawn’s destination square.

If any of these conditions fails, the capture is not legal.

Effect on the position

The en passant capture is unusual in that the captured piece is removed from a square different from the one the capturing piece lands on. This makes en passant the only chess move where a piece is captured without being on the square the capturing piece moves to. The capturing pawn ends up on the square the two-advanced pawn “passed over” — the square it would have stopped on if it had only advanced one square — and the captured pawn is removed.

The notation for en passant captures in algebraic notation usually adds “e.p.” after the move (e.g., dxe3 e.p.) to disambiguate, though in modern computer notation the “e.p.” annotation is often omitted because the move is unambiguous from the position alone.

Why the rule exists

The two-square initial pawn move was added to chess in roughly the fifteenth century as part of a series of speed-up rules — the queen’s modern long-range movement was added at the same time. Before the two-square advance, pawns moved only one square at a time. An enemy pawn on an adjacent file could always capture a pawn that walked past it, because pawns capture diagonally one square and a pawn could not jump over an attacker.

The two-square advance broke this symmetry: a pawn could now leap past the attacker. En passant was created to restore it — the attacker is given exactly one move’s grace to capture the leaping pawn at the square it would have stopped at under the older rules. The rule is, in the language of game theory, a patch that preserves an invariant the original rules guaranteed.

Common questions

Can I capture en passant after the position has been on the board for several moves? No. The right exists only for the move immediately after the two-square advance.

Can I capture en passant with a piece other than a pawn? No. Only pawns can capture en passant.

What if making the en passant capture would expose my king to check? The capture is illegal in that case, same as any other move that exposes your king.

Is en passant always optional? Yes. You are never required to capture en passant; you may simply make another legal move and the right disappears.

The rule has been part of formal chess rules since the modern codification of the rules in the seventeenth century. It is one of the few chess regulations that has not changed in any meaningful way during the modern era, and is referenced as the canonical example of how a rule can solve a structural problem in a game without disrupting its strategic balance.