2...Bb7

The idea

After 2...Bb7, the bishop hits e4, and White must decide how to protect it. 3.Bd3 is the most common, with 3.Nc3 the main alternative. Black then chooses between ...e6 with ...c5, ...Nf6 with ...d5, and the dangerous ...f5.

Plans for White

Defend e4 with a piece rather than with f3, which weakens the kingside. With Bd3 or Nc3, White develops while keeping the center, then plays Nf3 and castles. White's aim is to keep the center strong enough that the bishop on b7 has nothing to hit.

Plans for Black

Develop around the bishop: ...e6 to open the f8 bishop, ...Nf6 to add pressure on e4, and ...c5 or ...d5 to challenge the center. Black's king usually castles kingside after ...Be7 or ...Bb4.

Watch out for

For White, e4. It is Black's target, and if it falls with tempo Black's bishop on b7 becomes very strong.

For Black, falling too far behind. White has a big center and quick development, so if Black spends too long on pawn moves White can break through with d5 or e5 before Black's king is safe.