Ruy Lopez Theory

After the main moves in Ruy Lopez Theory: 1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. 0-0,
Why does Black always play 5...Be7 before 5...b5? Does it matter if Black switches the move order?

Correct me if I'm wrong, but I believe the delay on ...b5 is because White is not threatening to win e5 after Bxc6 until after Re1. So Black only plays b5 after Re1.

Generally this doesn't matter since the lines transpose and both sides are usually still well in theory at this point. But from a theoretical point of view, it's customary to only play ...b5 once the threat is somewhat real.

Doesn't seem critical to me. Most games transpose after Re1.

I think in general Black avoids creating the weaknesses associated with the b5 push until required. In the normal move order, white protects e4 (usually with Re1), thus compelling Black to decide how to defend e5. delaying b5 also leaves the option for White to exchange on c6, giving Black the bishop pair.

I dug around a little bit to see what I could find out, since I also play the black side of the Ruy, and I do play that move order generally. (Learning lots of theory was never my strong point!)

It turns out that 5... b5 is played a fair bit, but the follow up in top-level games is usually not 6... Be7, it's generally played with ideas of Bc5 or Bb7 instead.

All the same b5 followed by Be7 has been played a fair number of times as well, and it does not seem to be disastrous in any way. Most white players do in fact continue 7 Re1 transposing right back to the normal lines, but it looks like other things esp 7 d4 and 7 c3 are possible, and might possibly score better than Re1.

People have played b5 first against the likes of Fischer, Tal & Alekhine and come out with a draw, so it can't be that bad!

Ivanchuk played it against Shirov and won in this one...

http://www.chessgames.com/perl/chessgame?gid=1464697

So it seems to be a reasonable move at least.

Be7 or b5 usually transposes. Perhaps Be7, differently from b5, threatens Nxe4, when White will have to exchange its B for the N on c6 to regain the pawn. That's why White plays Re1 in response (in the mainline). You can play b5 instead of Be7 with other ideas in mind, like Bc5. If you play first b5 then Be7, White can transpose with Re1 or choose another move, but it's not dangerous for Black.