En passant is the one capture in chess where the captured piece is not on the square you move to. It lets a pawn capture an enemy pawn that has just moved two squares and landed beside it, as if that pawn had moved only one. Below is the rule in full, with examples checked move by move, and then puzzles from real games where en passant is part of the solution.
Four conditions must all be true. First, your pawn must be on its fifth rank: the fifth rank for a white pawn, the fourth rank for a black pawn. Second, an enemy pawn on a file next to yours must have moved two squares forward from its starting square in a single move. Third, that two-square move must land it directly beside your pawn. Fourth, you must capture on the very next move. If you play anything else first, the chance is gone for good for that pair of pawns.
The capture itself is diagonal, like any pawn capture. Your pawn moves to the square the enemy pawn skipped over, and the enemy pawn is removed from the square where it stopped. The name is French for "in passing", because you capture the pawn as it passes your pawn.
The rule exists because of the two-square first move. Without en passant, a pawn could use that double step to slip past an enemy pawn that would otherwise have been able to capture it. En passant keeps that capture available for exactly one move.
After 1.e4 Nf6 2.e5 d5, White's pawn stands on e5 and Black's d-pawn has just jumped from d7 to d5, landing beside it. White can now play 3.exd6, written 3.exd6 e.p. The white pawn goes to d6, the square the black pawn skipped, and the black pawn on d5 is taken off the board.
Change one detail and the capture disappears. If White plays 3.Nf3 and Black 3...Nc6, then 4.exd6 is illegal: the chance lasted one move only. And if the black pawn had reached d5 in two single steps, d7 to d6 and then d6 to d5, there is no en passant at all, because it never made a two-square move.
En passant is optional. Like any capture you can decline it, unless it happens to be your only legal move. Only pawns can capture en passant, and only pawns can be captured this way. It is available to both sides, on any file, and it can come up more than once in a game with different pawns.
Like every move, it is illegal if it leaves your own king in check, and en passant has an unusual way of doing that because two pawns leave the same rank at once. Put a white king on a5 and a white pawn on b5, with a black rook on h5. If Black plays c7 to c5, White cannot capture en passant: bxc6 would clear both b5 and c5, and the rook would then give check along the fifth rank. Remove the rook and the same capture is legal.
In a written position, the fourth field of a FEN string records the square behind a pawn that has just made a two-square move. That is how software knows en passant may be possible. There is more on the format in FEN chess notation explained.
In a puzzle, en passant is rarely the whole point. More often it is the move that opens a line, removes a defending pawn, or brings a pawn one step nearer promotion, and the rest of the combination follows from it. Sometimes the opponent's two-square pawn move is the move played just before the puzzle starts, and the capture is available for that one move only. Sometimes en passant gives check, or opens a line for a discovered check.
These positions are not common, because the conditions line up only occasionally. They also turn up more in stronger players' games than in beginners' ones. The trainer gives you the en passant puzzles closest to your rating, and solving them moves the same rating as Puzzle Training.
The most common is forgetting that en passant exists and treating an enemy pawn as safe after its double step. The second is trying to capture a move too late. The third is capturing en passant without noticing that it opens a rank, file or diagonal towards your own king. In puzzles there is a fourth: missing that the opponent's last move, the one played before you start, was a two-square pawn move that gives you the capture.
Before each puzzle, look at the move that was just played. If it was a pawn moving two squares next to one of yours, en passant is on the table. To play it on the board, move your pawn diagonally onto the empty square behind the enemy pawn. If you are stuck, the hint shows the piece first, then the move. After you solve, the full line appears beside the board.
For mixed tactics at your level, use Puzzle Training. Puzzle Storm trains speed, and the Woodpecker Method repeats a fixed set until the patterns are automatic. Elo Maxing serves the motif you are weakest at, and Pattern Drill works from positions in your own games. Pawn races often end in promotion puzzles, and en passant that opens a line is a cousin of the discovered attack.
A special pawn capture. When an enemy pawn moves two squares from its starting square and lands beside your pawn, your pawn can capture it by moving diagonally to the square it skipped over.
Only on the move straight after the enemy pawn's two-square advance, and only with a pawn standing on its fifth rank next to it. One move later the right has gone.
No. It is an option like any other capture. You only have to play it if it is your only legal move.
No. Only a pawn can capture en passant, and only a pawn that has just made a two-square move can be captured this way.
Because the conditions line up only occasionally in real games. The puzzles you get are the ones closest to your rating, so they may be a little easier or harder than usual.