Queen's Indian Defense, Spassky System

The Spassky System is identified by advancing White’s e2-pawn to e3. In algebraic notation, a pawn move uses its destination square, so 4.e3 means White plays e3 on the fourth move. The advance opens the diagonal for the f1-bishop and reinforces the d4-pawn. White often continues with the bishop on d3 and kingside castling, the combined king-and-rook move that carries the king toward the corner, before choosing a more committed plan.

The structure is flexible. The c1-bishop may later develop through b3 and Bb2, while the b1-knight can go to c3. Depending on Black's response, White may advance e4, play d5, or maintain the tension. Black normally fianchettoes with ...Bb7 and challenges the center with ...c5 or ...d5. Black may also check with ...Bb4+, forcing White to choose how to block.

Flexibility is not passivity

The move e3 frees the bishop, but the same pawn needs a second move to reach e4. White therefore needs to coordinate the pieces before preparing that advance. If White only maneuvers, Black may equalize space with a central break. If the timing is good, the system produces rich positions in which both sides change the structure according to circumstances.

The Petrosian Variation spends a tempo on a3 first to prevent ...Bb4. The Spassky System allows that check and uses the tempo to free the f1-bishop.