4.c4 Nb6

The idea

After 4.c4 Nb6, White has pawns on c4, d4 and e5, and Black's knight sits on b6. White chooses between the Exchange Variation, 5.exd6, and the Four Pawns Attack, 5.f4, the most ambitious.

Plans for White

Decide how much to build. Exchanging on d6 gives a sound position with more space; f4 gives a huge center that Black must attack at once. Either way, White's pawns give a space advantage.

Plans for Black

Hit the center with ...dxe5 or ...Nc6 and ...Bf5 or ...Bg4. The knight on b6 attacks c4, and Black's pieces are aimed at d4. Black must be active, because a slow game favors White's space.

Watch out for

For Black, the d5 push. If White gets d5 in, Black's knights can be cut off and pushed back.

For White, the c4 and d4 pawns. They are targets for Black's knights and bishops, so be ready to defend them.