Question about the move "Bb5" in the Ruy Lopez?

Hey, everyone. I'm not at all new to Chess, but I'm still working on improving, and there's a lot of theory that I'm not familiar with in common openings.

In the Ruy Lopez, what is the point of white's bishop to b5? I mean, yes, it threatens the defender of the e5 pawn, but black can easily defend that. 

It seems like trading your light-square bishop (which is sometimes white's stronger bishop early on) for a knight just to double black's pawns is a bit strange.

So, my question is why bishop b5? What is the idea(s) behind this move? 

it just puts pressure on the Knight, usually it reroutes to a4 and then b3 or c2 to support a kingside attack

You are inconveniencing black with their development. You will either take the Knight and damage the pawn structure or will find a retreated position for the Bishop on c2 behind the c3 pawn to target the King side in a future attack. So the bishop is sacrificed for the Knight in one line or it draws forward queen side pawns before maneivering to a sheltered staging post in another line where you intend to use pieces to overwhelm Black's King side.

#1

"In the Ruy Lopez, what is the point of white's bishop to b5?"
1) Developing the bishop into play
2) Preparing O-O and later Re1
3) undermining the control of Nc6 over central square d4, thus preparing d4

"I mean, yes, it threatens the defender of the e5 pawn"++ No it does not attack pawn e5. 3...a6 4 Bxc6 dxc6 5 Nxe5 Qd4 or 5...Qg5 is excellent for black 

"It seems like trading your light-square bishop (which is sometimes white's stronger bishop early on) for a knight just to double black's pawns is a bit strange."
++ White gets a won pawn ending, but black gets the bishop's pair. It is equal.

"So, my question is why bishop b5? What is the idea(s) behind this move?" ++ Most players retreat the bishop: 3...a6 4 Ba4. The bishop gets an active post on b3 or on c2.

I love how you say “bb5 *in* the ruy lopez” like bb5 isn’t the ruy lopez

The thing is, without Bb5 it's not the Ruy Lopez. I'm not sure whether this is better than Italian or bishop opening with Bc4 (or Bf4 after d4 😬). Or Larsen or Kia with bishop fianchetto...

Hi,

Yes the center pawn is 'easy' to defend, but an alternative defense introduces weaknesses in black's camp or inhibits development. For example, you really don't want to play Bd6.
And given the available tempi, black is too late capturing down the center lane with the queen because of the O-O - Re1 threat.

The Ruy is simply a very quick way to develop. There's no time to lose.
A better question is, what not to get about it?
Even after a6 - Ba4 in the Columbus or Morphy Defense you will soon have a fully operational Fischer bishop in place.

I suggest to do a course about it and study the lines - the 'point' of it all will follow when you see the resulting pressure on black's kingside.

Castling quickly and getting your king safe is of paramount importance. By playing 2. nf3, you've already developed one kingside piece, and must develop the other kingside piece, the light squared bishop, in order to achieve this goal. That being said, white has a few options in regards to development of this bishop.

Playing Be2 is an awfully passive move, so it is almost never played (Relegating a piece to obscurity on move 3 is not what you're looking for as white). 

Playing Bd3 shouldn't even be considered, as you'd just be hampering your own development and throwing any advantage you had with the white pieces away. 

Ba6 is obviously just a blunder. 

The only other truly viable option besides Bb5 is Bc4, which develops the LSB to an active square where it will put lasting pressure on the weak f7 square for as long as it remains there. In this way, you'd be developing a piece actively whilst also preparing kingside castling, thus achieving your goals in the opening. 

In comparison, Bb5 is considered to be more positional than Bc4. Instead of immediately attacking a weak square near black's king, playing Bb5 will result in a small positional advantage. By playing Bb5, you inherently put pressure on black's e5 pawn, thus making any central push with d4 much more potent. You also force black to respond to the central threat, unlike in the Italian where black can continue development with any move. White also threatens to cash in on a structural advantage early by playing an early Bxc6, which doubles black's queenside pawns and gives white a slight advantage in an endgame. Is this worth the Bishop for knight trade that you're concerned about? I would say yes, as you'd be trading two pieces of equal value but you'd also be gaining a slight advantage. The evaluation of the opportunity cost will be different for everyone, though. I'd also say that playing Bb5 is more about the central pressure it creates rather than just a threat to capture the pawn straight up. White's also not forced to trade the piece if black kicks it either. White can always just play Ba4 > Bb3 or Bc2 and practically put the piece on the same diagonal it would be on in the Italian anyway. 

My two cents

The bishop does put pressure on the knight which defends the pawn. There is no immediate threat of winning the pawn as after 4. Bxc6 dxc6 5. Nxe5, the reply 5...Qd4 regains the pawn. But there is pressure on the knight, and the threat is something that black must deal with. Lets say your opponent plays random moves after 3. Bb5 for example, 3...h6 4. 0-0 g6 5. Re1 b6  then you have 6. Bxc6 dxc6 7. Nxe5 and look at the position just from whites perspective. You are up material (1 pawn), you are ahead in development (Knight, and Rook are out), and your king is safe. Even though you had to give up the light squared bishop, their are a lot of positives for white and being up a pawn can win the game in the long run.

#11
"Lets say your opponent plays random moves after 3. Bb5 for example, 3...h6 4. 0-0 g6 5. Re1 b6  then you have 6. Bxc6 dxc6 7. Nxe5 and look at the position just from whites perspective."
++ That is no argument. Black is no goldfish and does something useful too.
3...a6, 3...Nf6, 3...d6, 3...Bc5, 3...f5, 3...Nd4, 3...g6, 3...Nge7 all have their merits.
The main point of 3 Bb5 is that it facilitates a later d4.

You know, folks have answered this, but the main thing is you have asked the "why" question. "Why" has to be asked throughout any game.

#14
Lasker and Fischer said so: to punish black for the tempo loss 3...a6.
https://www.chessgames.com/perl/chessgame?gid=1258181
https://www.chessgames.com/perl/chessgame?gid=1044389

Here is a more recent Giri game:
https://www.chessgames.com/perl/chessgame?gid=2041840 
the point of the delayed exchange and its apparent tempo loss 4 Ba4 6 Bxc6 is that black has played 4...Nf6 and 5...Be7, while in the exchange he needs ...f6 and ...Bd6 to overprotect central pawn e5.

when playing bb5, the opponent will eat your bishop after u have eaten the opponents knight then your knight can eat a pawn for free

I said that to place emphasis on the move. So what, should I have asked what the point of the Ruy Lopez is, instead?