You are right tafl, 5..a6 is not bad for the reasons you give ,a flexible and still useful in somes lines, for examples against Bc4. Somes guys did the error to play 6.Bc4 but that's bad, 6.Bd3 should be the main move, and if White devellops logically, and doesn't fall in the trap to play too agressive, but have a good use of Black's drawback of a6: even if they will play b5-Bb7, it's a little loss of tempo early on the game against a gambit. But I repeat : I was myself looking at a6 for Black some months ago with a good opinion on it, because it's still an underrated defense and quite rare, but not bad at all. But sorry to deceive you tafl but 5..a6 has a name : the Gedult defense :p

Just to add somes ideas: 6.Bd3 is not the only move (Ne5; Bg5 have been played; Bc4 too but I don't like it at all) and here If I was Black, maybe I would play 6..g6 with the idea to play the Bogoljubob (other choices are also good, like Bg4 for example, or Nc6 where Bb5 isn't available this time.) where the bishop is better on c4 than d3, d4-pawn is more a target here, that compense the loss of tempo a6 in the bogoljubov here.

One person early in the list of replies mentions "laziness".  I would play 2...e6 not due to laziness, but because you give me a French Defense, White or Black, and my rating is about 200 points higher.  My official rating is 1989, but it's more like 2200 after 1.e4 e6 2.d4 d5 as either color, and 1850-1900 otherwise.

But the BDG expert on CC: Peter Leisebein plays a3 with good results after having tryed the Zilbermints gambit and having analysed it as -/+ for Black. But who knows, maybe we can improve his analysis on the Zilbermints gambit to have a playable game but it's not easy.

Ok, if Black has equalized in the Leumberger Rasmussen attack : 4..Bb4 afther the best play by Black, it doesnt mean that White are worse, it mean they have equal chance also, right?If White have equal chance, I dont think it's a sort of refutation of the BDG. And if a GM play on this way with Black, I would not have more chance to win with another standard opening where the GM is better prepared, and stronger player. And it's not lame chess, it's just another interesting way of playing.

Ok TopNotch you did not understand my point, maybe because my english is not perfect (Iam just learning it at school) When I say solid here, it is not with the idea to survive, because effectively if I only play to survive here, your pawn up should finish to kill me in an ending. When I say solid here, it's about the most solid choice, to still have an attacking play without being "refuted" like in the Zilbermints gambit. I have played a "slow" move here but I am still ambitious after 8.a3 !

Actually I dont think Zilbermints gambit is really sound against the best defense, but it was an interesting choice. It's for that after 7..Nc6 8.a3 should be the "solid" choice.

Hehe very interesting MNb, you mark a point here I will analyse your response and if you are right, it would mean that I only should play normal theory when I face dxe4 in the French, or to change my way of playing against the French with a Diemer-Duhm or Alapin but I don't like so much theses pseudo-BDG. 

1.d4 d5 2.e4 e6 3.Nc3 dxe4 4.f3 Bb4 !? have been played also, and it doesnt look bad either. Is 4..e5 stronger? 

I will look at your "improvements", it looks really interesting.

If you like the Caro, let's imagine : 1.d4 d5 2.e4 c6, ok it his actually the starting position of the Caro but after Nc3, main move, black plays 3..dxe4 and now 4.f3 enter in the BDG Ziegler defense if he take the pawn, or enter in a type of game that the BDG player want even if you doesnt take on f3. Against the french, White can't force Black to reach a BDG, but there is some pseudo-BDG like the Alapin, the Diemer-Duhm, or if Black plays system like the Rubinstein : 1.d4 d5 2.e4 e6 3.Nc3 dxe4, the BDG player can try to enter in the Euwe defense of the BDG with 4.f3. And if he plays the classical French with 3..Nf6, then standard french move 4.Bg5, and again, if he take on e4 I play f3, and can transpose in the Euwe, and if he plays the MacCutchon or Be7, then I play normal french with White, that a BDG player should know also.

I like 1.d4 d5 2.e4 e6 as well. 

I agree with MNb that the Blackmar-Deimar is not quite sound, but I like to win games rather than test my memory.  The French allows me to do this.   

Occasionally I face 1.e4 c6 2.d4 d5 3.Nc3 de4 4.f3.  In those cases, I try for ...e5 at the earliest feasible moment.  I have had great success with the French and this line of the Caro-Kann, but (fortunately) I haven't faced the BDG against strong experts or masters in serious play.  Maybe there's a reason for it?

Gunderam (5...Bf5) looks very good now!  I think 4...c6 and 5...c6 are also good and relevant to transpositions from the Caro-Kann.  However, looking at the game Schoupal-Bonsai has steered me even more towards the opinion that 5...Bf5 is probably be the most effective way to meet the BDG.  Also 4...Bf5 (recommended by Wahls) doesn't look bad either.  But here I am beginning to think that 5...Bf5 is the most effective and least complicated solution!  You have two good choices:  Bonsai's approach and Markovich's recommendation.  I am little surprised that I am only one who has voted for this move.   

A funny observation:  When the BDG supporters start claiming a draw for White, I think that is often a good sign that White is having serious problems.  It kind of reminds the scene in Monty Python and the Holy Grail where King Arthur is fighting the Green Knight (or was he black?!), and after this absurd fight sequence, the Green Knight says, "We'll call it a draw."  And as King Arthur walks away, the knight is taunting him, "Chicken!  Chicken!  I'll bite you with my teeth!" (or something very similar).  I am joking, but this sometimes reminds me of die-hards who get a little carried away.  Sometimes I wonder in some cases if the same person was given the same position without knowing it was the BDG, if they would be so supportive of the white side.

Well, I would not chicken out of accepting the Blackmar-Diemer Gambit.  If I were Black, I would play the Teichmann Defense Accepted, 5...Bg4  6 h3 Bxf3  7 Qxf3 c6.

What is your favorite way of meeting the BDG ?