Key ideas
- 5.f3 protects e4 for good and takes g4 away from Black's knights and bishop. It also prepares Be3, Qd2 and sometimes Bh6 to exchange Black's best bishop. The cost is that the g1 knight loses its natural square and develops to e2, which slows White's kingside development.
- After 5...O-O 6.Be3, Black has three main approaches. 6...e5 usually leads to a closed centre once White plays d5, either at once or after 7.Nge2 c6. 6...c5 is the Sämisch Gambit: 7.dxc5 dxc5 8.Qxd8 Rxd8 9.Bxc5 Nc6 gives Black active pieces for the pawn. 6...Nc6 with ...a6 and ...Rb8, the Panno, prepares ...b5.
- When the centre closes after d5, White often castles long and attacks with g4, h4 and h5 to open the h-file, while Black looks for play on the c-file with ...c6 or a ...f5 break.
Plans for White
Complete the setup with Be3, Qd2 and Nge2, then choose between long castling with a kingside pawn storm and a slower queenside plan. Bh6 to exchange the g7 bishop is a standard idea once Black has castled short.
Plans for Black
Strike at the centre or the queenside before White's attack arrives. ...c5 and ...b5, sometimes as pawn sacrifices, are the most effective counterplay, because they open lines toward White's king if it has castled long.
For the wider picture, see the King's Indian Defense guide.