Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...Nd4/4. Nxd4/4...exd4/5. O-O

White castles.

Black has two main approaches, 5...Bc5, developing the kingside and supporting the advanced pawn, or 5...c6, gaining tempo on the bishop and supporting 6...d5 to expand in the centre. 5...a5 is a trap line.

5...Bc5 is most common. Black is lagging behind in development, so would like to prioritise getting their minor pieces out. It would be particularly good to develop their kingside pieces next, as this will help them to castle short. Unfortunately, since Black has already moved their pawn off e5, 5...Nf6? would run into 6. e5. The next best square for the knight is e7, but this would stop their bishop from developing. Therefore, Black develops their bishop first, then they intend to put their knight on e7 after it is out of the way.

White's will usually continue by closing the centre, 6. d3, giving their bishop room to develop.

Or, they can first play 6. Bc4, getting the bishop to a better diagonal and jumping before they are pushed. This move comes with tempo because it threatens Bxf7+ Kxf2 Qh5+ (forking Black's bishop on c5) to win a pawn: Black must defend their bishop with 6...d6.

5...c6 kicks the bishop and prepares ...d5. After 6. Bc4, 6...d5 can be played immediately, then after 7. exd5 cxd5 White can move the bishop back to b5. 8. Bb5+ Bd7 9. Re1+ Ne7 (Be7 loses a pawn to Qg4) and Black has difficulty developing his kingside, and will be vulnerable if they castle queenside.^[1] More common is 6...Nf6, intending to meet 7. e5 with the manoeuvre 7...d5!.

5...a5, forestalling development yet again, baits White into a trap. If White continues 6. d3?? automatically, then 6...c6 7.Bc4 b5 8.Bb3 a4 and the bishop is trapped.

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

1. e4 e5 2. Nf3 Nc6 3. Bb5 Nd4 4. Nxd4 exd4 5. O-O

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Wikipedia has related information at Ruy Lopez

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.