Why e3 in the QB setup?

Hey guys, I'm just wondering why white opts to play e3 in the Queen's Gambit setup? e3 blocks the black-squared bishops access, so why is e4 not played?

I know that the QG is a solid opening which many GM's play so I'm wondering if there is some sort of line where e4 could be a problem for white?

EDIT: QB? I mean QG...I swear I'm turning dyslexic.

e3 is sometimes a prelude to playing e4 later

I think the idea is that playing "3. e3" avoids the "3. ... Bg4 lines" and avoids the lines that occur after 3. Nf3 a6 4. e3 b5, which looks solid for black.

Possible continuation is 3. e3 e5 4. Bxc3 exd4 5. exd4 Nf6 6. Nf3. 

There's another post out there purporting to catalog the variations of QGA: http://www.chess.com/forum/view/chess-openings/every-opening-variation-you-need-to-know-of-the-qga

you could say that you develop your bishop when you move it outside the pawnchain before closing it with e3 but after something like this for example the bishop gets traded off early in the game anyway so why not wait a little bit before letting it out and the bishop is actually doing good things inside the pawnchain too in this situation

who am i to disagree with someone who probably know twice as much me about chess? i agree with the prinsiples you mention but my book by gm jakob aagard recommends this very line and after 3...Bd6 he comments "the simplest way of equalising, it has already been done!" so i think this is a exception to the rule.if not i think the londonsystem would have been alot more popular:)

Thanks for the informative variations. As a lowly rated player I have 0 opening theory.

I'm not just referring to QGA either. In fact, many opponents I face develop this way as if on auto-pilot when I go for my cowardly, 0 knowledge opening.

Here's an example opening I play versus d4. I'm not sure if this opening is sound or anything but developing Nd7 then pushing c5 has seemed like a good idea when faced with this opening.

Actually, several slav lines (and some semislav lines) include an early e3 before the queen's bishop is developed. Most other lines of the QGD have e3 after the queen's bishop has been developed.

i think this is a good way to battle d4, however if they are willing to play e3, i think the best reply is with e5 (instead of c5) for black, threatening to win a piece in the future and gain space with e4.   As for your initial post, e3 is usually played (following 1. d4) to strengthen the center and maintain an aggressive pawn on d4.  

I had no doubt you were aware of it. Others here might be less familiar.