Thanks pfren. Can you explain what you mean by 'understand a few things about resulting pawn structures'? Can you upload a game as example?
Philidor Defense: Is it worth playing as Black?

If White doesn't expect this opening, clearly he doesn't study chess openings at all. I get tired of hearing players parroting that line when discussing chess openings. In this information age you are not going to surprise any serious player at all inside of move 3 or 4. Anyone north of 1800 or so is going to have seen every opening sequence imaginable at one point or another. How deep White's preparation runs in the Philidor as opposed to the Spanish or Scotch or whatever White plays on 2...Nc6 is a different question. But with a few exceptions the lines are not sharp and both players can get by just by - as pfren said - knowing the resulting pawn structures.

i had a buddy about your rating. Guy who loved to sac material like crazy. And he just loved playing the Philidor.
I once asked him why, he answered "Because white makes one wrong move, he can end up in a lot of trouble, fast!"

Thanks everyone! Indeed with a game as old and widely played as chess, objective surprises within first few moves of it! There is a gambit variation in this line: the Philidor Gambit. I wonder if that enjoys as even reputation as the Philidor defense for Black. Simply the options are statistically so high after every move, it gets difficult to come to any final verdict in many situation. But personally, I see I must learn a good deal about it. I only wish if I had access to any standard lesson on it. The DVD suggested by pfren looks tempting, but alas I can not afford it at the moment. I may have to learn it the hard way by actually losing a lot many games!

Chesstempo database shows that 3...Nc6 is most common against 3.Bc4 lines. However, more common is 3.d4 when ...exd4 is most successful for Black (least win rate for white).
I think most modern Philidor players play the pirc move order

I must disagree with the main concept - that the Philidor is much less common than the Spanish. At the low levels of play there are an enormous percentage of players who think either exactly that or that playing the Spanish is too complicated for them. For these reasons, (and possibly others) 2...d6 is played nearly as often as 2...Nc6. Don't be one of those idiots. The Philidor is passive and offers White an easy game even if he has never seen it before. Taking your opponent out of theory is only useful if in the resulting position logical moves aren't strong. It is objectively sound but not practically strong; the latter being of far greater importance in sub-master level play.

best way to play against the philidor is to strangle it and not through complications
I completely agree. Simple, logical developing moves will give White a great position with more space and development than Black. In fact, I can't think of a single advantage that Black possesses (although that doesn't mean that there are actually none).

I respectfully disagree with PFren. The Philidor defense is not "completely ok".
It is possible to reach equality in almost any opening that doesn't drop material, but the task is made more difficult when Black plays passively from the very beginning.
The Philidor is rarely played by top grandmasters because the defensive task is thankless, and rarely results in anything better than a draw for Black.
The Philidor is even worse as an option for players rated below 2000. They often get extremely passive positions and are lost by move 20.
That leaves room for players between about 2000-2400 to play the Philidor successfully. There are a few cute traps in the Philidor that will attract some players, and there are some nice move order tricks that can be used. But this isn't really a great way for anyone with strong aspirations to make GM to play.
Here's probably the most famous game ever played using the Philidor Defense. Black can definitely improve on this game, by playing less aggressively than 3...Bg4? But this game shows the sort of problems Black faces.

The counter-gambit is very dangerous. I've seen many games where black fell to Legal's Mate while trying do a Philidor.

Yes, I could show miniature victories to match yours every time. Because, white tends to win more miniatures than Black in the Philidor. Oh, and White tends to score much better against the Philidor than average.
In games between players rated +2500, White scores about 62% (44% wins, 40% draws, 16% losses in my big database).
GMs tend to play the Philidor only in rapid and blitz time controls, but even including those, I only have 296 games in my database between players rated +2500. That is out of more than 187,000 games, not including correspondence games, between such players. That accounts for about .17% of games played by grandmasters. That is, about 1 out of every 600 GM games features a pure Philidor (the position after 1.e4 e5 2.Nf3 d6 3.d4)
Grandmasters, who make professional decisions about their repertoires, generally do not play the Philidor in games that matter.
So, go ahead and bombard us with miniatures. I'm sure the readers here are smart enough to figure out that a few miniatures don't show the whole truth, especially when a) the game is by transposition and b) the winner is more than 100 rating points higher to begin with.

I must disagree with the main concept - that the Philidor is much less common than the Spanish. At the low levels of play there are an enormous percentage of players who think either exactly that or that playing the Spanish is too complicated for them. For these reasons, (and possibly others) 2...d6 is played nearly as often as 2...Nc6. Don't be one of those idiots. The Philidor is passive and offers White an easy game even if he has never seen it before. Taking your opponent out of theory is only useful if in the resulting position logical moves aren't strong. It is objectively sound but not practically strong; the latter being of far greater importance in sub-master level play.
Black avoids tactics in the opening which usually arise after trying to protect the e5 pawn and this allows him to get developed safely. It isn't intended to 'trick' White. Some players with the White pieces play 1.e4 e5 2.Nf3 Nc6 3.d3 to get Philidor stuff with reversed colors.

I agree with IM Pfren in defending the Philidor as playable. Attacking players below IM level can't defeat this defense easily if black is serious on this defense. I lose more as white. Morphy humiliated this defense because his opponent was a patzer.

Avoid tactics? Like this:
Ummm, sorry, but you failed. This is not a Philidor, since in the Philidor there's a knight at f6 somewhere between move two and four.
Well, the rest of the world, including ECO, considers this to be a Philidor (C41). It is actually a fairly common line in the Philidor.
Here's the complete game:
[ECO "C41"]
[PlyCount "23"]
1. e4 e5 2. Nf3 d6 3. d4 Nd7 4. Bc4 c6 5. Ng5 Nh6 6. a4 $1 Be7 7. Bxf7+ Nxf7 8.Ne6 Qa5+ (8... Qb6 9. a5 Qb4+ 10. c3 Qc4 11. Nc7+ Kd8 12. b3) 9. Bd2 Qb6 10. a5 Qxb2 11. Bc3 Qb5 12. Nc7+ 1-0

Playing 1.e4 and following up with d3 is not a Philidor in reverse. Playing 1.d4 d5 2.Nf3 is not the reverse of a Marshall Opening (1.d4 d5 2.c4 Nf6?!). It happens to be a bit better for white.
I agree, if white plays 2.d3, white is about equal. The better player will usually win.

"Reversed Philidor", Carlsen, M. - Caruana, F. 1-0 :
http://www.chessvibes.com/reports/carlsen-takes-down-caruana-moves-to-2nd-place-in-bilbao
Fabiano Caruana vs Magnus Carlsen 1/2-1/2
http://www.chessgames.com/perl/chessgame?gid=1628882
Magnus Carlsen vs Shakhriyar Mamedyarov (0-1)
http://www.chessgames.com/perl/chessgame?gid=1671655
Sergey Karjakin vs Magnus Carlsen 1 - 0
http://www.chessgames.com/perl/chessgame?gid=1716694
And how many of those games were blitz games?
That Carlsen throws away the advantage of the first move as white quite often isn't news. Calling 1.e4 e5 2.d3 a "reverse Philidor" is a bit of a stretch though.

1.e4 e5 2.Nf3 d6 3.d4 Nd7 isn't good even if Black "remembers" to flick in c6. The knight on d7 makes Black's light squares vulnerable to cheapos. I'm pretty sure Tal beat every opponent that ever dared to block in their light-squared bishop this way against 1.e4. Black can try:
a) 1.e4 e5 2.Nf3 d6 3.d4 exd4 4.Nxd4 Nf6 5.Nc3 Be7 6.Be2 (6.Bf4) O-O
OR
2) 1.e4 d6 2.d4 Nf6 3.Nc3 e5 4.Nf3 Nbd7 and now 5.g4 is the only way White can stop Black from just developing and castling.

I have a book by Irving Chernev dated 1946 published by Chess Review of New York and it's the 2nd printing.
Of the 300 opennings it has 11 Philidor Defense opennings, plus twice as many variations that show how Black either gets mated, losses the Queen or material.
It seem like it is easier for white to win against the Philidor Defense. I think it's a losing defense.
The legal mate is a easy to apply when someone uses this defense.
We are not talking about masters using the Philidor defense, a way lower rated player has posted the question we are discussing.
Since this book is 68 years old I'm sure that there have been many other variations that have been tried that are better and might be acceptable.

The response of Black to 1.e4e5 2.Nf3 is popularly 2...Nc6, however 2...d6 is less popular. This defense bearing the name of Philidor is said as risky and often leads to sharp complications. One of the classical type of risk is evident from the following game where Black is check mated very soon.
The above game has been played many times and still it is common for Black to fall victim. However, my experience in Live Chess with this opening as Black has been a mixed one, winning often, probably because many players playing White do not expect this opening!
Experienced players, please give your comments and share games with this opening as Black! Let us understand if it is worth playing as Black or not!