The Philidor Defence is a chess opening characterised by the moves (in algebraic notation) 1.e4 e5 2.Nf3 d6. Named after the 18th century player François-André Danican Philidor, it has a repuation as being solid if somewhat unambitious.

White usually plays 3.d4, when Black has several options. 3...exd4 is one of the most common; after 4.Nxd4 Nf6 5.Nc3, Black normally plays ...Be7 and ...O-O with a characteristically solid but passive position, but can also fianchetto his bishop on g7 (Bent Larsen tried this in a few games, including a draw against Mikhail Tal in 1969).

The other main option for Black is to maintain the central tension and adopt a setup with Nbd7, Be7 and c6. A common line is 3...Nf6 4.Nc3 Nbd7 5.Bc4 Be7 6.O-O (6.Ng5 is an interesting alternative: after 6...O-O 7.Bxf7+ Rxf7 8.Ne6 Qe8 9.Nxc7 Qd8 10.Nxa8, white is material up, but Black can develop a strong initiative after, for example, 10...b5 11.Nxb5 Qa5+) 6...O-O 7.a4 (to prevent ...b5) 7...c6.

A more aggressive approach for black is 3...f5 (after 3.d4), a move which Philidor himself recommended. This can lead to more open positions than the other lines, but is less often seen.

A third move for Black which is generally considered to be not good is 3...Bg4. This was played in the famous "opera box game", when Paul Morphy continued with 4.dxe5 Bxf3 5.Qxf3 dxe5 6.Bc4, and White had better development and the initiative.

An alternative approach for White is to play 3.Bc4, and either delay d4 or forego it altogether and instead play d3.

As of 2004, there are no top players who employ the Philidor Defence with any regularity, although Etienne Bacrot and Liviu-Dieter Nisipeanu have occasionally experimented with it.