The Slav Defense is a chess opening that begins with the moves:

1. d4 d5

2. c4 c6

The Slav is one of the primary defenses to the Queen's Gambit. Although it was analyzed as early as 1590, it was not until the 1920s that it started to be explored extensively, although Steinitz essayed it in the first official World Chess Championship of 1886. Many masters of Slavic descent helped develop the theory of this opening, including Alapin, Alekhine, Bogoljubov, and Vidmar.

The Slav received an exhaustive test during the two Alekhine–Euwe World Championship matches in 1935 and 1937. Played by 11 of the first 13 world champions, this defense was particularly favored by Euwe, Botvinnik, and Smyslov. More recently the Slav has been adopted by Anand, Ivanchuk, Lautier, Short, and other top grandmasters, including use in six of the eight games that Vladimir Kramnik played as Black in the 2006 World Championship (in the other two, he played the related Semi-Slav Defense).

Today the theory of the Slav is very extensive and well-developed.