Nimzo-Indian Defense

The Nimzo-Indian Defense, often shortened to the Nimzo, arises after 3...Bb4 and is classified in ECO as E20 to E59. Aron Nimzowitsch brought it into master practice in the early twentieth century. The bishop sortie pins the c3-knight, so White cannot play an immediate e4 because the knight no longer guards that square. It also threatens ...Bxc3, saddling White with doubled c-pawns. Unlike most Indian defenses, Black does not fianchetto at once, though ...b6 and ...Bb7 often follow to reinforce control of e4. Because Black delays committing the center pawns, the opening stays flexible and can transpose into Queen's Gambit or Queen's Indian structures.

Black is usually willing to hand over the bishop pair. In return Black gets the static weakness of the doubled c-pawns and influence over d5 and e4, even when White recaptures on c3 with a piece. Black's task is to keep the position closed, blockade the White center and blunt any kingside attack. White aims to open lines for the bishops and build a broad center. The Botvinnik–Reshevsky game from the 1948 World Championship illustrates Black's plan: Reshevsky stopped White's kingside play with ...Ne8 and ...f5, left White's bishops and queen passive, and won the endgame.

The natural 4. Bd2 breaks the pin but is rarely seen at top level because it is unambitious. On Lichess the most frequent replies are 4. Nf3, the Three Knights Variation, and 4. Qc2, the Classical Variation, where the queen is ready to recapture on c3 and avoid doubled pawns. The Rubinstein System, 4. e3, develops quietly before White picks a plan. Gligorić and Portisch did much to shape its theory. Black chooses mainly among 4...O-O (the Normal Variation), 4...c5 and 4...b6 (the St. Petersburg Variation). After 4...O-O, the Reshevsky Variation 5. Ne2 lets White recapture on c3 with the knight. In the Hübner Variation, 4...c5 5. Bd3 Nc6 6. Nf3 Bxc3+ 7. bxc3 d6, Black takes on c3 voluntarily and sets up a dark-square blockade. Fischer used it against Spassky in 1972.

The Sämisch Variation, 4. a3, forces the bishop to decide at once, and the Kmoch Variation, 4. f3, prepares e4 directly. Less common tries include the Leningrad Variation 4. Bg5, the Spielmann Variation 4. Qb3, the Romanishin Variation 4. g3 and the Dilworth Gambit 4. e4.

The defense is held in high regard at every level, and every world champion from Capablanca onward has played it. Many White players sidestep it with 3. Nf3 or 3. g3. After 3. Nf3, the check 3...Bb4+ (the Bogo-Indian) can be met with 4. Bd2 or 4. Nbd2. Engine assessment of the starting position is close to equal, and online results are nearly even.