Key ideas
- 4.Bd2 is the main line. Black can keep the bishop with 4...Qe7 (the Nimzowitsch Variation) or 4...a5 (the Wade-Smyslov Variation), exchange with 4...Bxd2+, retreat with 4...Be7, or counter at once with 4...c5 (the Vitolins Variation).
- 4.Nbd2 (the Grünfeld Variation) blocks with a knight and prepares a3 to ask the bishop to take or retreat. If it takes on d2, White keeps the bishop pair.
- After the bishop trade Black often sets up with ...d6 and ...e5. The Retreat Variation (4.Bd2 Be7) with ...d5 instead leads to Queen's Gambit or Catalan positions, since White likes to play g3 and Bg2.
Plans for White
Recapture on d2 in a way that helps the centre, often with Nbxd2 or Qxd2, and prepare e4. A kingside fianchetto with g3 and Bg2 adds pressure on the long diagonal.
Plans for Black
After trading the dark-squared bishop, put pawns on dark squares with ...d6 and ...e5, develop with ...Nc6 or ...Nbd7, and castle short.