Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nf6/3. d4/3...Nxe4

3...Nxe4 is the main continuation. Black takes on e4 and is temporarily a pawn up. White will, now or soon, recapture on e5 and then it is a trade of pawns.

Before taking the pawn, it is usual for White to play the intermezzo 4. Bd3, attacking the knight. Usually Black defends it with 4...d5, and then White recaptures the pawn 5. Nxe5. However, it is actually unnecessary to defend the knight right away, as if it is taken Black can recover it tactically: 4...Nc6 is the Murrey variation and if 5. Bxe4!? d5! 6. Bd3 e5 forks the knight and bishop, recovering the material. Nevertheless, 4...d5 is the main move as Black is able to take part of the centre while opening lines for his bishops to develop.

Taking the pawn back immediately with either the knight or the pawn is possible.

4. dxe5 is also playable and comes with its own flavour. Clearing the d-file threatens Qd5, from where the queen may trap Black's knight and form a battery against f7 with Bc4, so Black usually responds 4...d5, controlling the d5 square with their queen.

After 4. Nxe5 d5 5. Bd3 the position transposes to the main line.

For explanation of theory tables, see theory table and for notation, see algebraic notation.

1. e4 e5 2. Nf3 Nf6 3. d4 Nxe4

When contributing to this Wikibook, please follow the Conventions for organization.

Wikipedia has related information at Petrov's Defence.