Is this checkmate?

tackleberry

http://www.chess.com/echess/game.html?id=55202900

I won this game by resignation, apparently, but it looks like I should have won by checkmate - am I missing something? 

Scottrf

He can take the pawn en passant.

http://en.wikipedia.org/wiki/En_passant

goldendog

en passant

tackleberry

En passant! 

Thanks guys. I have a real blind spot for that. 

ChessisGood

Yep, after 23...axb3 24. axb3+ Na4 and 25. Rxa4#, 25. Nc6#, 25. Qb4#, and 25. b4#. The most beautiful, in my opinion, is 25. Qc7#

Also, I believe that 24. a4 works as well, as Black cannot defend.

ChessisGood

Oh, you mean right there...No, he can take en passant.

Jett_Crowdis

technically it is mate, but not in the current position. after 23. b4+ axb3 24. axb3+ Na4 25. Qc7#