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The Benoni Defense is a group of chess openings generally characterized by the opening moves 1.d4 c5 2.d5 although Black's ...c5 and White's answer d5, is often delayed until move 2 or 3. The most usual opening sequence for the Benoni is 1.d4 Nf6 2.c4 c5 3.d5. Black can then sacrifice a pawn by 3...b5 (leading to the Benko Gambit). If Black elects not to sacrifice he usually plays 3...d6, 3...e6 or 3...g6 leading to the mainline Benonis.

There are many variations of the Benoni.

The most common is the Modern Benoni, which may come after the moves 1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nc3 d6 5.e4 exd5 6.cxd5 g6 or 1.d4 Nf6 2.c4 c5 3.d5 e6 4.Nc3 exd5 5.cxd5 d6 6.e4 g6. Black will fianchetto his king's bishop to g7 and castle, playing for an attack on the queenside and the semi-open e-file. White will play for a central initiative. Compared to the usual lines of the King's Indian Defense, Black's fianchettoed bishop is a lot more active since it is not blocked by a black pawn on e5. However, not having the pawn on e5 makes White's center more fluid. The Modern Benoni is thus a very combative and double-edged opening, indeed, it is one of the most double-edged openings with 1.d4. Many White players who fear the sharp battles decide to avoid the Benoni all together; after 1.d4 Nf6 2.c4 c5 they play 3.Nf3 leading to a quieter variation of the English Opening.

The Old Benoni arises if Black immediately answers 1.d4 with 1...c5. The Old Benoni frequently transposes to the Modern Benoni or Czech Benoni, but there are a few independent variations.

In the Czech Benoni Black does not fianchetto his king's bishop and he plays his king's pawn to e5. One possible move order is 1.d4 Nf6 2.c4 c5 3.d5 e5. The Czech Benoni is much more solid than the Modern Benoni, but it is also more passive.

"Benoni" is a Hebrew term meaning "son of sorrow". The opening was named by Aaron Reinganum in 1825 who analyzed the opening in a time of sorrow.