Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nc3/3...Nf6

Queen's Gambit Declined
	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/ppp2ppp/4pn2/3p4/2PP4/2N5/PP2PPPP/R1BQKBNR
	Moves: 1. d4 d5 2. c4 e6 3. Nc3 Nf6
	ECO code: D35-D69

3...Nf6

With 3...Nf6, Black begins developing the minor pieces, gets closer to castling, and exerts control over the center.

This is the classical main line of the Queen's Gambit Declined. White has several options, though some of these may transpose into each other at some point.

4. cxd5 is the exchange variation. Unlike other exchange variations notorious for yielding a quiet game (e.g. French, Slav), this exchange results in what is known as the Carlsbad pawn structure, which has several aggressive plans, such as a "minority attack" on the queenside. Although it was once relatively uncommon, as Black's usual response 4...exd5 unblocks the queen's bishop from development, it has become the main line after 3...Nf6.

4. Bg5 is a classical continuation that leads to a wide variety of positions. White gets the dark-squared bishop outside of the pawn chain in order to be able to release the light-squared bishop with e2-e3. Black usually unpins the knight with 4...Be7 and tries to castle quickly. After the usual 5. e3 O-O 6. Nf3, Black has a major choice between 6...Nbd7 (the classical variation) and 6...h6. 4...Nbd7 is a notable alternative, often leading to the Cambridge Springs defense (5.e3 c6 6.Nf3 Qa5).

4. Nf3 is the three knights variation. White gives Black many choices on how to continue development, including some of the most aggressive variations of the Queen's Gambit, such as the Semi-Slav (4...c6) and Vienna (4...dxc4) variations, as well as the Ragozin (4...Bb4) and Semi-Tarrasch (4...c5). Transposition to the 4. Bg5 line after 4...Be7 5. Bg5 is also possible, but White has the major alternative of 5. Bf4, the Harrwitz Attack.