20 ( +1 | -1 ) miazaris absolutely correct....however, it is much more fun to wait for the endgame when the pawn has advanced to the seventh rank and is about to be queened, and then claim it en passant from thirty moves ago !!!
89 ( +1 | -1 ) reasonI also read somwhere about the reason of taking en-passant existence.
Originally (long time ago) the pawns could only move one square also from their initial position. But the game flow was wery slow because of it so they changed it and chess became more dinamical. But the pawns gained more power and a rather 'unfair' ability to avoid capture. That's why en passant rule was brought into game. And the fact that the pawn 'jump' is actually a comprimation of two moves is also the reason why you can take te pawn only immediatly in the next move - assuming that that in the following moves the pawn would leave it's fictional position in the third(seventh) rank.
Hope it's correct - if I'm wrong I would be glad if someone more experienced would correct me so I wouldn't keep nonsense in my head.
27 ( +1 | -1 ) Here is an example of en passant board #610875 move 13 in a recent game that I had. I took one of my opponents pawns en passant, which ultimately resulted in him losing the game, I guess he didn't see it.