"1. c4 b5"

This is the Jaenisch Gambit. I discovered this as I was thinking about responses to the English opening, and liked the character of it. It has a few notable qualities or traits;

• It takes the c4 pawn off of a place where it attacks d5
• It immediately allows one to fiancetto the c8 bishop if one is so inclined
• the hole at b5 can be used sometime in the future to place the rook behind and attack with
• It allows for an open, tactical game from the outset with its own unique character; the positions in which can be quite striking and fun to play
• It will catch the English player off guard

Brief introduction to playing the Jaenisch

There are two main approaches to playing the Jaenisch, however both expect the response of cxb5. The first is to delay attacking the pawn, which can be done in a few ways. The second, the most common, is to attack it immediately, either by ...a6 or, less frequently, c6. In any case, both sides often fianchetto and castle kingside and fight it out on the queenside. Strategically, it makes a good deal of sense, as Black will be spiriting it's king away from the messy queenside and White will, in addition to that reason, will also be attacking the point of his pawn advantage.

Though attacking the pawn immediately via 1.c4 b5 2.cxb5 a6 (3. bxa6) may be the 'mainline' for this opening, I far prefer delaying the attack until later in the game. The immediate attack does have its advantage in that the b5 pawn is difficult to attack with either but the c or a pawns, which may be more difficult to move later in the game, a sort of 'thorn in the side' scenario. (It is also interesting to note that this particular formation might be conducive to a sort of 'fortress' like formation on the queenside by advancing the c and a pawns up to or beyond the b pawn later on) To delay the attack on the pawn, several courses are available. ...bb7 is my favourite of them (and often c6 sooner or later, to be followed bxc6 nxc6 and often rb8 or rc8 later at my leisure), though d5, g6, nf6, and to a lesser extent, e5 and f5 (trying for almost a stonewall-esque position with d5, e3, f5 etc.) are all possible as well. Remember though that g6 and nf6 are liable to transpose into the other variations.

This should do for now. I'll get back to this later with more. If anyone has anything to add, it would be appreciated.

I like it!!  It's unorthodox and very post-hyper-modern.  I have a friend who plays exclusively English/Sicilian, so this will be very useful to me.

A couple of comments:

 In your sample game, after 17. .... Rxa5, you give 18. Rc1?  Why not 18. Rxa5! Qxa5 19. bxc6 winning a piece.  5 min analysis, so maybe I miss something......

 2d comment: Since one of your main points of playing the Jaenisch Gambit is to remove the c pawn from a square where it attacks d5, we should definitely analyze 1. c4 b5 2. c5 .... Since the pawn on c5 still quasi-attacks d5 (via the     en passant rule).  Call it the Jaenisch Gambit Declined. ...... Doh! I wish I knew how you posted the board with the draggable pieces, but I just got on this site yesterday.....  A'ight, in our heads then.  Forgive any mistakes in this very rough preliminary line.....

1. c4 b5 2. c5 d5  -- the most aggressive response, advantages: force white's hand immediately, because en passant can only be performed on the move immediately following the pawn advance. Drawbacks: an open file with a giant hole at c6. 3. cxd6 cxd6 4. d4 Nf6 5. Bf4 g6 6. Nf3 Bb7 7. N1d2 Bg7 8. Rc1 0-0 And my brain is tired (I'm not that great of a player....).  There you have it, the Jaenisch Gambit Declined, double fianchetto variation.  Basically, if I was black and I had decided to play the first 3 moves, the voice of my old master would be saying "Run, Luke! Run!!" in my head and I'd be trying to castle K-side as quick as possible, while still maintaining a somewhat hypermodern stance toward the center.  White's play reflects my desire, if I had been playing white, to get a rook on that juuuuuicy c-file as quick as mutantly possible, taking a classical stance on the center (without giving away my plans for the e-pawn) and a bit of fast development, with obvious strengthening of c4 and c5.  As white I would try to use to the c-file for an overwhelming attack.  As black, I would be concerned about protecting the b5-a6(eventually this move will be nescessary)-Bb7 complex, and try to prep my cetral advances of e5 and f5 as much as possible, trying to get in moves like a6, Kh8, Re8, and possible N8d7 or Nh5 to try and hit that center as much as possible.  Should be a fun game for both sides: fast, mean, and daring for white; cerebral, sneaky and manipulative for black: basically a game with all the aesthetic quality of an argument with my mother-in-law....... Joy!

Thanks DJHeilke!

No, you're not missing anything about Rxa5; I think my brain just preferred a walk in the park at that moment. ;) For the board with moving pieces, when making a post, just click on the little chessboard icon, which when moused over will say "insert position or game".

Hmm... I hadn't given too much time to thinking about the gambit declined. I do suppose however that moves other than cxb5 could also be useful to analyse. Perhaps a basic table might be good to organise our thoughts on the possibilities:

1.c4 b5 - Jaenisch Gambit

2. cxb5 - Jaenisch Gambit Accepted

  2... a6, c6 - Immediate challenge

  2... bb7 - fianchetto the bishop

  2... f5 - Jaenisch Stonewall 

  2... d5

  2... e5

  2... g6, nf6 - kingside activity/prep for castle

    (2... g6 3. h4 - the "Oh No!" variation)

2. c5 - Jaenisch Gambit Declined

  2... d5

  2... d6!?

  2... e5

2. b4 - Jaenisch Countergambit

2. Nc3 (If bxc4, white can gain very nice position, but 2... b4 3.Na4 makes both feel awkward) - Jaenisch Countergambit #2

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1. c4   b5
2. b4   bxc4
3. Nc3  d5
4. e4   dxe4
5. Nxe4 Be6
6. Bb2  Nf6
7. Nxf6+ gxf6
8. Qf3  

1. c4   b5
2. cxb5 d5
3. e4   dxe4
4. Nc3  Nf6
5. d4   exd3
6. Bxd3

It's a wing gambit...

I would just take the pawns, it seems black is going for some sort of benko-gambit like pressure here but white has a MUCH better structure (he hasn't moved anything besides the c-pawn) than in the benko. 

I would just take the pawn if I were white too. Perhaps we're all just greedy.

Here is a game played in the mainline for illustration:

It seems that in all the games in which Black does not lose, he manages to concentrate his forces somehow, get them working together, usually in the centre.