Nimzo-Indian Defense, Three Knights Variation

The Three Knights Variation is defined when White's king's knight moves to f3, written Nf3 in algebraic notation. The name counts developed knights for both sides: Black's knight is on f6, while White's are on c3 and f3. The move develops a piece, controls central squares, and prepares castling, the special move involving the king and a rook.

Black keeps several replies. Advancing the queen's pawn to d5 may reach a Queen's Gambit structure; advancing the c-pawn to c5 keeps a more typical Nimzo-Indian struggle; b6 prepares the bishop for b7. White's plan must adapt to the structure that actually appears.

When a sequence reaches a familiar position from another opening, it is called a transposition. This variation therefore rewards looking at the board before the label. It can also connect with the St. Petersburg Variation if e3 and b6 follow.