Nimzo-Indian Defense

The Nimzo-Indian Defense arises with White pawns on d4 and c4 and a knight on c3, while Black plays ...Nf6, ...e6, and ...Bb4. The bishop on b4 pins the c3-knight to the king: if the knight moves, the b4-e1 diagonal opens toward White's king.

That pin helps discourage e4 because the c3-knight is one of that square's natural supporters. Black may exchange the bishop for the knight and give White doubled c-pawns, meaning two white pawns on the c-file. In return, White keeps the bishop pair, meaning both bishops, one moving on light squares and the other on dark squares, while Black has surrendered one bishop. The strategic question is whether the pawn weaknesses matter more than the power of the two bishops.

The pin leads to the Nimzo-Indian imbalance

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StartBb4a3Bxc3+bxc3

...Bb4 prepares an absolute pin on Nc3 and makes the e4 advance, which that knight helps support, more difficult.

Nc3 gives Black's bishop a target

Black can influence the center without committing another pawn yet.

1. ...Bb4 prepares an absolute pin on Nc3 and makes the e4 advance, which that knight helps support, more difficult.

The Nimzo-Indian is flexible because Black has not yet fixed the entire pawn structure. If White plays Nf3 instead of Nc3, Black often chooses related defenses such as the Queen's Indian Defense or Bogo-Indian Defense.