Advance Variation, Euwe Variation

The Euwe Variation postpones the usual 5...Qb6 in favor of the bishop move. Black will almost always play ...Bd7 at some point anyway, so making it now keeps the queen uncommitted until White's setup is clear. In some lines ...Qc7, adding pressure to e5, suits Black better than ...Qb6. The bishop can also later leave the pawn chain via b5 or a4, a standard way to solve the problem of the French bishop. The move was already known to Greco in 1620, and Viktor Korchnoi popularized it in the 1970s. It is now regarded as a main line.

The move order matters most against 6. a3. With the queen not yet on b6, the pawn move has less purpose, and theory holds that 6...f6 lets Black at least equalize by striking at the center at once. White more often chooses 6. Be2 or 6. dxc5, and online the most frequent reply is 6. Bd3. The pin attempt 6. Bb5 fails to 6...Nxe5. The engine rates the position as roughly balanced, and Black scores slightly better than White in online games.