3Nf3

3Nf3 is a chess move notation indicating that, on White's third move, a knight moves to f3. In standard algebraic notation it is written as 3.Nf3; the version without the period, 3Nf3, is sometimes seen in PGN files or informal sources. The move typically refers to the knight from g1 heading to f3, a standard development square early in many openings.

The primary purpose of 3.Nf3 is developmental: it brings a knight to a central, active square, supports control of e5 and d4, and prepares kingside castling. It also preserves flexibility, allowing a variety of pawn structures and plans depending on Black’s reply.

3.Nf3 appears in a wide range of openings. In the Nimzo-Indian Defense, after 1.d4 Nf6 2.c4 e6, White often plays 3.Nf3. It is also common in the Queen's Indian Defense, Grunfeld Defense, and King's Indian Defense, as well as many Queen's Pawn structures. Because it is a natural developing move, it frequently leads to transpositional possibilities among Reti, English, and other flexible systems.

Notation-wise, 3.Nf3 is unambiguous on move 3 since only the g1 knight can reach f3 from its starting position. If ambiguity arises later in a game (in rare cases), disambiguation would be added (such as Nbd2 or Nf3, specifying the originating knight).

Overall, 3.Nf3 is one of the most common, versatile third moves for White, underpinning a broad family of strategic setups and transpositional possibilities.