What do you play against the London System?

Possibly helpful:
Grandmaster Repertoire 11: Beating 1 d4 Sidelines by Boris Avrukh (2012)
https://web.archive.org/web/20140627001415/http://www.chesscafe.com/text/hansen164.pdf

Dealing with d4 Deviations by John Cox (2005)
https://web.archive.org/web/20140627032909/http://www.chesscafe.com/text/hansen89.pdf

I have refuted the Craplondon system. Game over GingerGM and Cyrus Lakdawala.

You are right jengaias, I thought it was impossible, but I did it again.

Seriously tho, the London is a good opening, but Im tired of all those crappy authors talking it as the brand new opening that is easy and crushes black because that is not the case. I also find it crappy that it is hard to find good info on how to deal with it as Black. I think this is all a monopoly-

I play this as an anti-london KID.

Against the London I play the KID or the QID, depending on my mood. The same as playing against the Stonewall Attack.

I play a Slav-type defense against it which is somewhat a mirror-image.

If you're a premium chess24 member, Jan Gustaffsson has a fantastic series dedicated to handling d4 sidelines like the London system, where he advocates 1.d4 Nf6 2.Bf4 d5 3.e3 c5 (safer maybe to go e6 immediately to avoid all dxc5 shenanigans since the recommendation is an e6 based setup anyways.) 4.Nd2 Nc6 5.c3 e6 6. Nf3 cxd4 7.exd4 Nh5!? ( of course 7.cxd4 is an option to go for a drier game) and he gives the mainlines after 6..Bd6 as well as an alternative. I prefer this setup over the QID lines where I sometimes feel overly passive. 

I agree. They always say that you don't have to learn anything, that you can be lazy AF and always get a fierce kingside attack. Every game against a london player is always the same. 

As AKJett stated, there are 2 lines that are the most challenging for London players:

1. The ...Qb6 Defense

2. The King's Indian Defense

Though the KID is "the acid test of the London System", it doesn't get a clear advantage for Black, but it makes finding a plan difficult for White. London players often use a different option against the KID, such as The 150 Attack, The Barry Attack, or The Jobava Attack.

3. A Classic Setup: (good for when White uses an odd move order to transpose into the London or if White uses a move order that makes ...Qb6 ideas look bleak.)

It might seem boring to play in the classic setup, but it's like playing against a Stonewall, so if you're comfortable with handling Stonewalls, you should be fine.

Interesting thread.  An anti-LS group think.

Hope our group can enjoy.  Regards, Joe 

https://www.chess.com/club/londoneers

I had read a thread here about how some people, when they see the London System being played against them, just resign, because they expect to be crushed. But if it's largely passive and defensive, it makes no sense that it would have that kind of reputation. And it's a good thing Caruana didn't try playing it in the current WCC too in that case.

Wow, I just took a look at the New In Chess link for the book by Kiril Georgiev. 
https://www.newinchess.com/fighting-the-london-system

The blurb states, "Grandmaster Kiril Georgiev has been the strongest Bulgarian player for many years. He was a Junior World Champion and a bronze medalist in Europe."

and yet he's never been the strongest Bulgarian player in terms of rating. Remember, Bulgaria boasts Veselin Topalov and they used to have another +2700 player, Igor Cheparinov (who is now representing Georgia). More to the point, he is currently playing under the Macedonian flag! It would be true to say he's the strongest Macedonian player. 

EDIT: Apparently, at least according to Wikipedia, he was Bulgaria's strongest player long before Topalov came on the scene. My apologies. The FIDE records don't go back that far.

london system i play everything and win against it. opening irrelevant. its about ability

The more I look at the Georgiev book, which is only 196 pages, the more I like it! It's very short, but it gives good explanations of White's basic plans of development and how Black can counter them. He discusses the latest theory at the time of writing and points out lacunae in the literature. It's very readable, and is probably useful for any club player up to about 2200 strength. 

It's a useful introduction to the opening and gives some good advice on where a stronger player can start doing his own research into the variation. 

As Georgiev points out in the intro, the critical lines all lead to 0.00. But the point of the London is that it offers a broad range of branching out points which allows both players to go wrong. The London takes an anti-computer approach to the game, and the book shows that. There aren't many lines to memorize, but there are many thematic ideas. 

https://www.newinchess.com/media/wysiwyg/product_pdf/7724.pdf

That is a sample.  The book is available on Amazon and other outlets.

The best I can ...

I play london...