1. d4 d5
2. c4 c6

The great disadvantage of the standard Queen’s Gambit Declined for black is that 2… e6 locks in the queen’s bishop. The Slav Defence, then, takes the reasonable approach of defending the pawn on d5 from the other side, with 2… c6. Recall also that in the Queen’s Gambit accepted, when black takes on c4, they have no real prospect of holding on to that extra pawn; in the Slav Defence, however, dxc4 may become a real threat, since black can play b5 and have a solid pawn chain (c6-b5-c4) protecting the c4 pawn. The disadvantage, as compared to the QGD, is that black is playing on the wing and white has a chance to take control of the centre.

The main line has both sides developing knights: 3. Nc3 Nf6 4. Nf3 (see diagram above). Then black has three main options:

1. The “pure” Slav, 4… dxc4. Here, black takes the pawn that was originally gambited but, unlike in the QGA, may be able to hang on to it.
2. The Chebanenko Variation, 4… a6. Here, black plans to play b5, forcing white’s pawn on c4 to make up its mind to either advance or be exchanged.
3. The Semi-Slav, 4… e6. This (at least temporarily) locks in the queen’s bishop, but black typically plans to eventually play b5 and develop the bishop to b7. This variation can lead to some deep tactical battles.

If white doesn’t like these possibilities, an option is to avoid the main line with 3. cxd4 cxd4, the exchange variation. This, however, tends to lead to a boring, drawish position. Another option is 3. e3, but this locks in white’s queen’s bishop.

The Slav Defence was analyzed as early as 1590, but was rarely played for centuries. Steinitz played it in the first official world championship match in 1886, but it was not until the 1920s, when it was analyzed by players like Alekhine, Bogoljubov, and Alapin (all of Slavic descent, hence the name) that it gained real popularity. It remains a common opening today.