3Bb4

3Bb4 refers to Black’s third move Bb4 in the Nimzo-Indian Defense, typically occurring after 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4. In this usage, the bishop on b4 pins White’s knight on c3 to the king on e1, creating immediate pressure on White’s central control and influencing how White may resolve the pin.

Origin and purpose: The Nimzo-Indian Defense was developed in the early 20th century and became one of Black’s most respected responses to 1.d4. The move 3...Bb4 is designed to exercise positional constraint by pinning the c3-knight, which often slows White’s ability to maintain a free, solid center. It also invites Black to develop smoothly with pressure along the central and queen-side dark squares, and it provides a flexible platform that can transpose into various lines depending on White’s reply.

Typical continuations: White has several common ways to proceed. 4.Qc2 is a popular unpinning idea that keeps options open for both sides. 4.Nf3 continues development and supports central control. 4.e3 builds a solid center and prepares to recapture with cxd5 or to develop fluently. Other responses include 4.g3, 4.a3, or 4.Bd2, each leading to distinct pawn structures and strategic plans. Black’s plan generally involves maintaining the pin, contesting the e4 and d4 squares, and gradually completing development with …d5 or …b6 in some lines.

See also: Nimzo-Indian Defense, chess opening theory, bishop pin concepts.