"en passant" in chess: Why the Move Was Invented and How It's Played

The move en passant is both interesting and perplexing to beginners. The move was originally invented in 1561, and officially accepted to the rulebook in 1880 according to wikipedia.

"en passant" means "in passing".

Here is a clear explanation of the en passant rule:

When a pawn moves two squares on one turn, on the very next move, an adjacent pawn may capture that pawn as if it had only moved one square.

The move was invented to prevent players from locking up the chessboard with pawns. In the diagram below, black moves his pawn 2-squares, and past the white pawn.

If the en passant rule didn’t exist, players could end up with positions like this!

That would create very boring games! I remember when I first started playing chess, this happened a few times until I learned this very unique rule.

Each pawn will only have two opportunities to en passant, but can only take one of them. But it can be played whenever the position allows, namely a pawn moving to the 5th rank next to an opponent's pawn.

When a pawn is near the opponent’s side (on the 5th rank) and another pawn moves two squares to land beside it, you can apply the en passant rule.

You can capture the pawn that jumped two squares by moving directly behind it, as if it had only moved one square - not two. It is a capture so you will remove the pawn off the board even though you are moving behind.  

Elliott Neff, who appears in the above video, wonderfully explains the history and reasoning for this move in his Knight Level DVD along with many other important topics in this second in a series of chess training DVDs.