Today at the second round of the Internal Competition of Het Kasteel (Chessclub in Wijchen, The Netherlands) I played Black. My opponent came with 1. e4. My reply was 1. ... - c5, The Sicilian Defence. A couple of moves later, we came in the Rossolimo Variation. I never played this before.....

I know... my Qa5+ is not good, but I wanted to move out my Queen. Because I want to place the Queen on b6 later, to avoid that white can Castle and that the Queen was aiming on g2.

But what is the idea behind the Rossolimo Variation? How to play a good defence againt this opening? I must say... White is very poor in this, so this might not be a good example for this opening....

Not sure about the Rossolimo (there are lots of good opening books out there).  But in response to your 14th move, your opponent should've played 15 Bxe7.  After 15... d3 16 fe de 17 Qd6 he's a piece up.

My reference book refers to it as the anit-siccilian and only has lines for white whithout detailing proper responses for black, which was dissapointing enough, but I'm really not a fan of this when playing black.

I wish I had some input but I do look forward to hearing some more about this position.

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Yes, I see now, that taking the pawn with the Knight was not good. But fortunate for me, he didn't see. At the analizing of the game, my opponent told me that he loves the Knights. I think that that's the reason why he took my Knight instead of my Bishop. I prefer in such games the Bishop.

a lost game for black. . should white take the bishop first.  a nice opening.nxe4 passive move. suicidal.

You're correct, as far as I can see, about your early Queen journey.  The Rossolimo gets difficult early.  White tries to set up a picket fence of pawns in the center and black tries to control the advance in order to catch up with development instead of space.  You sweat a lot, early in the game, no matter which you pick. 

Since I grew up playing the Dragon, I'll, usually, play 3 ... g6 instead of e6. It cuts down the sensible choices for white to O-O or BxN.  Try John Emms book in the Starting out series from Everyman press, the Sicilian.  It's not extensive, or exhaustive, but the chapter on the Bb5 systems - the Rossolimo and the Moscow variations is very clear for starters.

But can anyone show me what the main line is of this opening? Then I can study about it. I guess that I should take the pawn instead of the Queen's move. Then move the Bishop at d7.

As far as I know this is it.  But, you might try Kasparov's games.  He seems to like it in exhibitions.  And, he's just slight a bit better than me.   But, (and this has varied over the years depending on how well both he and I were doing at the time) what's 1200 or 1400+ rating points among friends?

1 e4 c5, 2 Nf3 Nc6, 3 Bb5 g6, 4 O-O Bg7,

5 Re1 Nf6, 6 c3 O-O, 7 d4 d5, 8 e5 Ne4

Many books give 6 c3!  and 7...d5! both for grabbing the center

Just another quick note.  sometimes I'm slow checking out what sites have to offer.  However, I just went to the top of the page under the Learn section. hit book Openings and searched of Rossolimo.  Came up with 10 variations for study.

the rossolimo variation along with the certain lines in the Moscow variation aim to build the solid pawn center that white is often denied in the Sicilian while allowing smooth development and early castling . if you can see a slight resemblance between it and the Lopez your right as play in certain lines may closely resemble the closed lines of the lopez. Black should fear the doubling of his pawns as he receives the bishop pair in return. most players wouldnt bother to take anyway as preserving the bishop is often thought best . Black has two main strategies e6 aiming to play Nge7 supporting his knight or g6 aiming to counter whites center with a king side fianchetto . Play has been analyzed to be about equal and Bb5 as a whole is thought to be a drawing weapon but if black isnt prepared as in this case white can achieve a comfortable edge

your move 7, if going to play, ill move Nb3, followed by Be3 then Qd2. re group and develope your pieces.

If I was white, I wouldn't play this opening. I was playing black.

I use it against Sicilian playing OTB, have 2-1-1 balance with loss and draw against 300 higher rated and wins against equal. In both wins a got a good attack on King's side. It's more strategical and requires less memorizing than regular Sicilian which is exactly what I want. There is a good book - "The Sicilian Bb5 Revealed"  with a lot of strategic plans and interesting games.