The Pirc Defence (/ˈpɪərts/ PEERTS) is a chess opening characterised by the response of Black to 1.e4 with 1...d6 and 2...Nf6, followed by ...g6 and ...Bg7, while allowing White to establish a centre with pawns on d4 and e4.

The Pirc Defence is usually defined by the opening sequence This is the most commonly played line after Black responds to 1.e4 with 1...d6.

[2] It has been claimed to give rise to somewhat interesting and exciting games,[3] where Black will have counterplay but has to be cautious about playing too passively.

[4] According to Garry Kasparov, the Pirc Defence is "hardly worth using in the tournaments of the highest category", as it gives White "too many opportunities for anybody's liking".

The opening began gaining some popularity only after World War II, and by the 1960s it was regarded as playable, owing in large part to the efforts of Canadian grandmaster Duncan Suttles.

[8] A distinction is usually drawn between the Pirc and lines where Black delays the development of his knight to f6, or omits it altogether; this is known as the Modern or Robatsch Defence.

The most frequently played move after 5...0-0 is 6.Bd3 (the Weiss Variation), with 6...Nc6 the most common response, though 6....Na6, with the idea of ....Nc7, ....Rb8 and ....b5 became popular in the 1980s after 6....Nc6 was found to offer Black few winning chances.

Efim Geller, Anatoly Karpov and Evgeni Vasiukov have all successfully used this system for White; Zurab Azmaiparashvili has scored well as Black.

It received a severe blow in about 1985, when Gennady Zaichik showed that Black could castle anyway and play a dangerous gambit with 5...0-0 6.Qd2 e5.

The Argentines feared the sally ...Ng4, though some British players (especially Mark Hebden, Paul Motwani, Gary Lane, later also Michael Adams) came to realise that this was mainly dangerous for Black, therefore playing Be3 and Qd2 in all sorts of move orders, while omitting f2–f3.

After 3...g6 4.c4, an unhappy Seirawan found himself defending the King's Indian Defence for the first time in his life,[11] though he managed to draw the game.