Pirc Defence, Main Variation, 5. Be3 line

I need some advice about playing this line of the Pirc Defence as Black by players with positional understanding of the game.

5.Be3 is quite a strong move. With his powerful centre, now White is aiming to Black's kingside, perhaps with a later Ng5. So, castling inmediately is not recommended here for Black.

The first time I had to face this as Black, I had little understanding of the Pirc Defence, so I didn't perform vey well:

I decided to make some research on this line, and found a book where they recommended playing ... c6 after 5. Be3. A possible line would be this one:

But searching in my chess games database, I found out that many GM's played 5... a6!? instead of c6, with the idea of playing b5 in the next move. Let's take a look at it:

Other top players such as Gurevich and Chernin, who are Pirc defence players, have also tried this line. So my question is, why should I play, 5... c6 or 5... a6? And, what are the strategic ideas behind the two lines?

The Pirc is a really hard defense to play.  Keep working at it!

We played Tiger Hillarp's a6 in response to the Austrian in the Premium Showdown chess match - go and check it out.

http://www.chess.com/votechess/game.html?id=7936390

The pirc is a very interesting defense. I have played it some, but I don't think it suites my style. Many people find it perfect for them though, and I have played a few of them.

Very nice post Freecat. Also, thanks for some good info Streetfighter.