Bb4

Bb4 is a move in chess notation where a bishop is moved to the square b4. The exact bishop is determined by which bishop can legally reach b4 in the position; if both bishops could reach b4, disambiguation is used (for example Bfb4 or Beb4).

In common openings, Bb4 figures prominently as Black’s development move in the Nimzo-Indian Defense. After 1.d4 Nf6 2.c4 e6 3.Nc3, Black plays 3…Bb4 to pin White’s knight on c3 to the king on e1. The idea is to exert immediate pressure on White’s center, disrupt White’s intended development, and provoke concessions such as doubled pawns or a compromised pawn structure if White chooses to resolve the pin with Bxc3 or a3 followed by Bxc3. A typical continuation is 4.a3 Bxc3 5.bxc3, which leads to a characteristic pawn structure and piece activity for Black.

Bb4 also appears in other openings as a flexible developing move to contest key diagonals, influence control of central squares, and prepare a variety of middlegame plans. For White, encountering Bb4 often requires careful handling: options include maintaining the pin with a move like Qc2 or e3, or breaking the pin with a3 and recapture strategies that shape the pawn structure.

Disambiguation is an important note in notation. If two bishops can reach b4, the origin file or rank is specified (such as Bfb4 or Beb4) to avoid ambiguity.

See also: algebraic notation, pin, Nimzo-Indian Defense, Bishop (chess).