Old Variation

Queen's Gambit

1.d4 d5 2.c4 dxc4 3.e3 e5 4.Bxc4 exd4 5.exd4

White plays 3.e3 to recapture on c4 with the bishop at once; Black strikes back in the center with 3...e5.

Fun fact: 3.e3 has often been employed by strong players, including Anatoly Karpov. Source

The idea

Instead of 3.Nf3, White plays 3.e3, opening the bishop's diagonal so it can take back on c4 straight away. Lichess calls this the Old Variation. Black's most direct answer is 3...e5, striking at d4 before White's pieces are out, and after 4.Bxc4 exd4 5.exd4 White has an isolated pawn on d4.

The line long had a harmless reputation because of 3...e5, but the open positions that follow have not proved easy for Black to handle in practice.

Plans for White

Develop quickly with Nf3, Nc3 and castling, and use the open lines. The bishop on c4 and a queen on b3 both aim at f7, and the isolated pawn on d4 gives White space and the squares e5 and c5 for the knights.

Keep pieces on the board: as in every isolated-pawn position, the pawn is a strength in the middlegame and a weakness in the endgame.

Plans for Black

Develop with ...Nf6, ...Bd6 or ...Be7, and castle, keeping an eye on f7. Then blockade the pawn on d4: a knight on d5 is ideal, and trading pieces makes the pawn weaker.

3...e6 is the quieter choice and usually transposes back to the main lines of the Classical Defense.

Watch out for

For Black, greed. After 3.e3, holding the pawn with 3...b5? runs into Salvio's trap: 4.a4 c6 5.axb5 cxb5?? 6.Qf3, and the rook on a8 falls or 6...Nc6 7.Qxc6+ wins a piece. 3...Be6 also holds the pawn, but White has good compensation after 4.Ne2.

For White, 4.dxe5? trades queens after 4...Qxd1+ 5.Kxd1, and White's king loses the right to castle while still a pawn down. 4.Bxc4 first, and only then decide about d4.