Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Ba4/4...Nf6/5. O-O/5...Be7/6. Re1/6...b5/7. Bb3

=Ruy Lopez Main Line=

Black is no longer under any direct threat and may continue developing - the king and c8-bishop still need to find better squares. Of the three natural moves,
 * 7...Bb7 is considered a sideline as it gives up the option of ...Bg4 (an option White usually spends a tempo cutting out by playing h3). If Black's going to put this bishop on b7 early on, she normally wants to have the other bishop on c5.

The main moves both carry threats of different types.
 * 7...d6 defends the e5-pawn a second time, freeing the c6-knight to come to a5 and swap off White's precious bishop, so it "forces" the move 8.c3 in response - a move White wants to play anyway.
 * 7...O-O allows Black to follow up with the Marshall Gambit: 8...d5. Of course, Black still has the option of 8...d6, and since in modern times 7...d6 is almost always followed by 8...O-O anyway, at first glance it seems that 7...O-O is a clear winner over 7...d6 in terms of giving Black options. That can't be entirely true, or no-one would play 7...d6. Firstly, the Marshall Gambit has been analysed to death, and if there's a way of proving it absolutely sound it hasn't been discovered yet. Secondly, White has a choice of ways of dodging it - 8.h3 steering the game back towards the main line, or 8.a4 eliminating the need to play c3.

Historically, 7...d6 was played with the intention of following up with 8...Na5 even if White did play 8.c3, but this has not been a popular line since the 1930s.