Semi-Slav Defense

The Semi-Slav Defense is a variation of the Queen's Gambit chess opening defined by the position reached after the moves:

1. d4 d5

2. c4 c6

3. Nf3 Nf6

4. Nc3 e6

The position may readily be reached by a number of different move orders. With Black advancing pawns to both e6 and c6, the opening resembles a mixture of the Orthodox Queen's Gambit Declined (QGD) and the Slav Defense.

Black is threatening to capture the white pawn on c4, and hold it with ...b7–b5. White can avoid this in a number of ways. About 80% of games continue 5.Bg5 or 5.e3: the former constitutes a sharp pawn sacrifice, while the latter restricts the dark-squared bishop from its natural development to g5. Other possible moves are 5.Qb3, 5.g3 and 5.cxd5 though after the latter 5...exd5 leads to a line of the QGD Exchange Variation where White's early Nf3 enables the Black queen bishop to freely develop, which should give equality (ECO codes D43 and D45).

For the Semi-Slav the Encyclopaedia of Chess Openings designates codes D43 through D49.