Pirc Defense

The Pirc Defense is based on the hedgehog concept. If you are playing black you are essentially inviting white to take as much space as he wants while you develop a somewhat cramped yet defensive position. If white takes too much space his position will become very difficult to defend and you can start targeting his vulnerable forward pawns and pieces. If white doesn’t take too much space black reserves space in the center to make central pawn moves which can shape a favorable position.
I find that the Pirc is very strong in blitz games but in longer games white has time to make better use of his extra space and development. I used to play the Pirc Defense quite a bit but now I stick mainly to a Sicilian variation.

Wikipedia - Pirc Defense
I am a little disappointed with the amount of information the Wikipedia has on the Pirc. It’s not that this is poor information, I just simply expected a little more. There are six variations that are accompanied by short descriptions. There is also an interesting game using the Pirc from 1983 between Karpov and Azmaiparashvili.

The Austrian Attack Trend
I really enjoy to play this position as white. Over the past 100 years it has over tripled in popularity. Here white usually plans to castle queenside and storm the kingside. Here is a brilliant example of the Austrian Attack. (Bobby Fischer vs. Pal Benko) Move 19 is very instructional. White plans to push the e pawn exposing a mating threat at h7. In order to defend this the black bishop must remain in place to defend by pushing the h pawn to h6. Therefore this allows the rook to move into the very favorable f6 square.

Die Pirc Die!
This is a very instructional site dealing with all recommended pirc variations.