Austrian Attack

The idea

After 4.f4 Bg7 5.Nf3 O-O, White has a broad center with pawns on d4, e4 and f4, aiming for the e5 breakthrough. Black has castled and will counterattack with ...c5 or ...e5. Wikipedia names 6.Bd3, the Weiss Variation, the most frequent continuation and 6.e5 a sharp try with unclear consequences.

Plans for White

Play Bd3, O-O and look for e5 at the right moment, driving the knight from f6 and opening lines toward Black's king. White's pieces stay behind the pawns, ready to follow them up. White's space is the main asset, and Jan Timman has played the Austrian successfully with both colors.

Plans for Black

Counterattack in the center before White's attack arrives. ...c5 hits d4, and ...Nc6 with ...e5 hits the center too. Wikipedia gives 6...Nc6 as the most common reply to 6.Bd3. Black wants White's pawns to become targets.

Watch out for

For Black, the e5 push. If it comes while the knight on f6 has no good square, Black is driven back and White's attack on the king gets going.

For White, the dark squares. With f4 and e5 played, e5 and the g1-a7 diagonal can become weak, and Black's bishop on g7 can come to life once the center opens.