Chess Opening Theory/1. d4/1...d5/2. c4/2...c6/3. Nc3/3...Nf6

Slav defence
a b c d e f g h 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 a b c d e f g h
Position in Forsyth-Edwards Notation (FEN) rnbqkb1r/pp2pppp/2p2n2/3p4/2PP4/2N5/PP2PPPP/R1BQKBNR
Moves: 1. d4 d5 2. c4 c6 3. Nc3 Nf6
ECO code: D10
Parent: Slav defence

3...Nf6

Black develops a knight to f6, and puts pressure on the e4-square. From here White has multiple good responses, although 4. Bf4 and 4. Bg5 should be avoided as Black can play 4...dxc4 and retain the pawn without giving White any compensation.

4. Nf3 develops the White's knight to f3, increasing control over the d4 and e5 squares. This is considered the mainline and it gives Black many responses to choose from.

4. e3 is similar to the Quiet variation, which occurs after 3. Nf3 instead. It disallows the Slav accepted with 4...dxc4 and forces Black into a different variation like the Semi-Slav or the Chebanenko Slav. It is however possible for Black to play 4...Bf5 and sacrifice a pawn. This move is usually followed up by 5. Nf3, although occasionally Nf3 is delayed in favour of other developing moves such as Qc2.

4. cxd5 is occasionally played, relieving tension in the center, and play transposes to exchange Slav variations.

Theory table

1. d4 d5 2. c4 c6 3. Nc3 Nf6

	4
Slav accepted	Nf3 dxc4
Semi-Slav defence	... e6
	e3 e6
Exchange variation	cxd5 cxd5	=

References

Wikipedia has related information at Queen's Gambit Declined.