The Nimzo-Indian Defence is a chess opening

Chess opening

A chess opening is the group of initial moves of a chess game. Recognized sequences of opening moves are referred to as openings as initiated by White or defenses, as created in reply by Black. There are many dozens of different openings, and hundreds of named variants. The Oxford Companion to...

 characterised by the moves:

1. d4 Nf6

2. c4 e6

3. Nc3 Bb4

Other move orders, such as 1.c4 e6 2.Nc3 Nf6 3.d4 Bb4, are also feasible. In the Encyclopaedia of Chess Openings

Encyclopaedia of Chess Openings

The Encyclopaedia of Chess Openings is a classification system for the opening moves in a game of chess. It is presented as a five volume book collection describing chess openings...

scheme, the Nimzo-Indian is classified as E20-E59.

This hypermodern

Hypermodernism (chess)

Hypermodernism is a school of chess that emerged after World War I. It featured challenges on the chess ideologies presented by central European masters, such as on Wilhelm Steinitz’ approach to the centre. It also challenged in particular the dogmatic rules set down by Siegbert Tarrasch...

 opening was developed by Grandmaster

International Grandmaster

The title Grandmaster is awarded to strong chess players by the world chess organization FIDE. Apart from World Champion, Grandmaster is the highest title a chess player can attain....

 Aron Nimzowitsch

Aron Nimzowitsch

Aron Nimzowitsch was a Russian-born Danish unofficial chess grandmaster and a very influential chess writer...

 who introduced it to master-level chess

Chess

Chess is a two-player board game played on a chessboard, a square-checkered board with 64 squares arranged in an eight-by-eight grid. It is one of the world's most popular games, played by millions of people worldwide at home, in clubs, online, by correspondence, and in tournaments.Each player...

 in the early 20th century. Unlike most Indian openings the Nimzo-Indian does not involve an immediate fianchetto

Fianchetto

In chess the fianchetto is a pattern of development wherein a bishop is developed to the second rank of the adjacent knight file, the knight pawn having been moved one or two squares forward....

, although Black often follows up with ...b6 and ...Bb7. By pinning White's knight

Knight (chess)

The knight is a piece in the game of chess, representing a knight . It is normally represented by a horse's head and neck. Each player starts with two knights, which begin on the row closest to the player, one square from the corner...

 Black prevents the threatened 4.e4 and seeks to inflict doubled pawns

Doubled pawns

In chess, doubled pawns are two pawns of the same color residing on the same file. Pawns can become doubled only when one pawn captures onto a file on which another friendly pawn resides. In the diagram, the pawns on the b-file and e-file are doubled...

 on White. White will attempt to create a pawn centre and develop his pieces to prepare for an assault on the Black position.

Black's delay in committing to a pawn structure makes the Nimzo-Indian (sometimes colloquially referred to as the "Nimzo") a very flexible defence to 1.d4. It can also transpose into lines of the Queen's Gambit

Queen's Gambit

The Queen's Gambit is a chess opening that starts with the moves:The Queen's Gambit is one of the oldest known chess openings. It was mentioned in the Göttingen manuscript of 1490 and was later analysed by masters such as Gioachino Greco in the seventeenth century...

 or Queen's Indian Defence

Queen's Indian Defense

The Queen's Indian Defense is a chess opening defined by the movesBy playing 3.Nf3, White sidesteps the Nimzo-Indian Defense that arises after 3.Nc3 Bb4. The Queen's Indian is regarded as the sister opening of the Nimzo-Indian, since both openings aim to impede White's efforts to gain full control...

. The Nimzo-Indian is a highly respected defence to 1.d4, is played at all levels and has been played by every world champion since Capablanca

José Raúl Capablanca

José Raúl Capablanca y Graupera was a Cuban chess player who was world chess champion from 1921 to 1927. One of the greatest players of all time, he was renowned for his exceptional endgame skill and speed of play...

. White often plays 3.g3 or 3.Nf3 to avoid the Nimzo-Indian, allowing him to meet 3.Nf3 Bb4+ (the Bogo-Indian Defence

Bogo-Indian Defence

The Bogo-Indian Defence is a chess opening characterised by the moves:-Variations:White has three viable moves to meet the check. 4.Nc3 is a transposition to the Kasparov Variation of the Nimzo-Indian, therefore the main independent variations are 4.Bd2 and 4.Nbd2.-4...

) with 4.Bd2 or 4.Nbd2, rather than 4.Nc3.

General considerations

In the Nimzo-Indian, Black is generally prepared to concede the bishop pair by playing ...Bxc3. As dynamic compensation, he often doubles White's c-pawns, which represent a static weakness, and gains play against the central light squares d5 and e4, even in those instances where White is able to recapture with a piece after ....Bxc3. Black will aim to close the position to reduce the scope of White's bishops. To this end, Black must blockade the white pawn centre from advancing and neutralise White's attacking chances on the kingside. An example of Black's strategy carried out successfully is the classic game Mikhail Botvinnik

Mikhail Botvinnik

Mikhail Moiseyevich Botvinnik, Ph.D. was a Soviet and Russian International Grandmaster and three-time World Chess Champion. Working as an electrical engineer and computer scientist at the same time, he was one of the very few famous chess players who achieved distinction in another career while...

 - Samuel Reshevsky

Samuel Reshevsky

Samuel "Sammy" Herman Reshevsky was a famous chess prodigy and later a leading American chess Grandmaster...

 from the 1948 World Championship Match-Tournament

World Chess Championship 1948

The 1948 World Chess Championship was a tournament played to determine a new World Chess Champion following the death of the previous champion Alexander Alekhine in 1946. The tournament marked the passing of control of the championship title to FIDE, the International Chess Federation which had...

, which reached the position in the diagram after White's 24th move.

Earlier in the game, Reshevsky was able to block White's kingside attack by playing ...Nf6-e8 and ...f7-f5. Now, both White's bishops are reduced to defence, and White's queen must go to the miserable a2-square to defend both the pawns on a3 and c4. Without any prospects for counterplay, White's game is strategically hopeless, and Black ultimately exchanged queens and won the endgame.

Rubinstein System 4.e3

The Rubinstein System (named after Akiba Rubinstein

Akiba Rubinstein

Akiba Kiwelowicz Rubinstein was a famous Polish chess Grandmaster at the beginning of the 20th century. He was scheduled to play a match with Emanuel Lasker for the world championship in 1914, but it was cancelled because of the outbreak of World War I...

) is White's most common method of combating the Nimzo-Indian. Svetozar Gligorić

Svetozar Gligoric

Svetozar Gligorić is a Serbian chess grandmaster. He won the championship of Yugoslavia a record twelve times, and is considered the best player ever from Serbia...

 and Lajos Portisch

Lajos Portisch

Lajos Portisch is a Hungarian chess Grandmaster, whose positional style earned him the nickname, the "Hungarian Botvinnik"...

 made great contributions to the theory and practice of this line at top level during their careers. White continues his development before committing to a definite plan of action. In reply, Black has three main moves to choose from: 4...0-0, 4...c5, and 4...b6.

In addition, Black sometimes plays 4...d5 or 4...Nc6. 4...d5 can transpose to lines arising from 4...0-0, but White has the extra option of 5.a3 (known as the Botvinnik

Mikhail Botvinnik

Mikhail Moiseyevich Botvinnik, Ph.D. was a Soviet and Russian International Grandmaster and three-time World Chess Champion. Working as an electrical engineer and computer scientist at the same time, he was one of the very few famous chess players who achieved distinction in another career while...

 Variation). This forces Black to retreat the bishop to e7 or capture on c3, which transposes to a line of the Sämisch Variation long considered good for White because he will undouble his pawns at some point by playing cxd5, eliminating the weak pawn on c4, then prepare the e4 pawn break, backed by the bishop pair, which will gain force in the more open type of position which will ensue. 4...Nc6 is the Taimanov Variation, named after Russian GM Mark Taimanov

Mark Taimanov

Mark Evgenievich Taimanov is a leading Soviet and Russian chess player and concert pianist.-Chess:He was awarded the International Grandmaster title in 1952 and played in the Candidates Tournament in Zurich in 1953, where he tied for eighth place. From 1946 to 1956, he was among the world's top...

. Black prepares to play ...e5, which may be preceded by...d5 and ...dxc4, or ...d6. The variation was tried several times by the young Bobby Fischer

Bobby Fischer

Robert James "Bobby" Fischer was an American chess Grandmaster and the 11th World Chess Champion. He is widely considered one of the greatest chess players of all time. Fischer was also a best-selling chess author...

, and has long been favoured by GM Nukhim Rashkovsky

Nukhim Rashkovsky

Nukhim Nikolayevich Rashkovsky is a chess Grandmaster and coach from Russia.His first meaningful chess moves were played at the Sverdlovsk Palace of Pioneers, one of many training schools for talented young players in Soviet Russia.He was a regular patron of the long-running Soviet Chess...

.

4...0-0 Main Line: 4.e3 0-0 5.Bd3 d5 6.Nf3 c5 7.0-0

Black's most flexible and frequently played response is 4...0-0. The main line continues 5.Bd3 d5 6.Nf3 c5 7.0-0, reaching the position in the diagram.

White has completed his kingside development, while Black has claimed his share of the centre. At this point, the most important continuations are:

7...dxc4 8.Bxc4 Nbd7 (Parma Variation)

7...dxc4 8.Bxc4 cxd4 9.exd4 b6 (Karpov Variation)

7...dxc4 8.Bxc4 Nc6 9.a3 Ba5 (Larsen Variation)

7...Nc6 8.a3 Bxc3 9.bxc3 dxc4 10.Bxc4 Qc7 (Main Variation)

7...Nc6 8.a3 Bxc3 9.bxc3 Qc7 (Khasin Variation)

7...Nbd7 (Averbakh Variation)

• The Parma Variation (7...dxc4 8.Bxc4 Nbd7) is named after Slovenian grandmaster Bruno Parma
  Bruno Parma
  Bruno Parma is a Slovene chess player and Grandmaster.Parma was born in Ljubljana, Slovenia . He first played in the World Junior Chess Championship in 1959, sharing second place...
  
  , and can sometimes transpose to the Karpov Variation if pawns are exchanged on d4. White usually continues with 9.Qe2, clearing the d1-square for the rook, which will assist in the advance of the d-pawn. Black then faces an important decision. He may play 9...b6, with the intention of playing ...cxd4 at some point to isolate the d-pawn and blockade it, or exchange on c3 as well to play against the isolated c3-d4 pawn couple. Or, he can consider 9...a6 to grab space on the queenside with ...b5. In this case, Black will usually retain his dark-squared bishop. Black also has two rare alternatives on his eighth move worth mentioning: 8...Qe7 intending ...Rd8 is the Smyslov Variation, invented by former World Champion Vasily Smyslov
  Vasily Smyslov
  Vasily Vasilyevich Smyslov was a Soviet and Russian chess grandmaster, and was World Chess Champion from 1957 to 1958. He was a Candidate for the World Chess Championship on eight occasions . Smyslov was twice equal first at the Soviet Championship , and his total of 17 Chess Olympiad medals won...
  
  , and 8...Bd7 followed by ...Bc6 is the Bronstein Variation, the brainchild of two-time world championship finalist David Bronstein
  David Bronstein
  David Ionovich Bronstein was a Soviet chess grandmaster, who narrowly missed becoming World Chess Champion in 1951. Bronstein was described by his peers as a creative genius and master of tactics...
  
  .

• The Karpov Variation, (7...dxc4 8.Bxc4 cxd4 9.exd4 b6) named after former World Champion Anatoly Karpov
  Anatoly Karpov
  Anatoly Yevgenyevich Karpov is a Russian chess grandmaster and former World Champion. He was the official world champion from 1975 to 1985 when he was defeated by Garry Kasparov. He played three matches against Kasparov for the title from 1986 to 1990, before becoming FIDE World Champion once...
  
  , is one of Black's most reliable defences to the Rubinstein System. For the moment, White has an isolated pawn
  Isolated pawn
  In chess, an isolated pawn is a pawn which has no friendly pawn on an adjacent file. An isolated queen's pawn is often called an isolani. Isolated pawns are usually a weakness because they cannot be protected by other pawns...
  
   in the d-file, even so, Black plans to play ...Bxc3 at some point and follow up with ...Bb7, ...Nbd7, ...R(a)c8 and ...Qc7 to restrain White's c- and d-pawns. After 7...dxc4 8.Bxc4 cxd4 9.exd4 b6 the game usually continues 10.Bg5 Bb7, when 11.Ne5, 11.Re1, 11.Rc1 and 11.Qe2 are all good moves for White.

• The Larsen Variation (named after GM Bent Larsen
  Bent Larsen
  Jørgen Bent Larsen was a Danish chess Grandmaster and author. Larsen was known for his imaginative and unorthodox style of play and he was the first western player to pose a serious challenge to the Soviet Union's dominance of chess...
  
  ) can be reached by either 7...dxc4 8.Bxc4 Nc6 9.a3 Ba5 or 7...Nc6 8.a3 dxc4 9.Bxc4 Ba5, but the latter move order gives White the extra option of 9.axb4. The idea is to wait until White plays dxc5 before playing ...Bxc3. If White does not oblige, then Black will play ...Bb6 with pressure on the d-pawn. The point of inserting ...dxc4 before ...Ba5 is to prevent White from inflicting an isolated queen's pawn (IQP) on Black by playing cxd5.

• The Main Variation was enormously popular in the 1950s, but the name has become increasingly inappropriate ever since. This is not because the line is bad for Black – on the contrary, Black equalises in all variations – but because White has a huge selection of moves to choose from, and Black must be familiar with all of them. After 7...Nc6 8.a3 Bxc3 9.bxc3 dxc4 10.Bxc4 Qc7, White has tried 11.Be2, 11.Bd3, 11.Ba2, 11.Bb2, 11.Bb5 (trying to provoke ...a6 before retreating the bishop), 11.h3, 11.a4, 11.Re1, 11.Qc2, and 11.Qe2 – ten possibilities in all! Regardless of the move chosen, however, the basic strategic ideas remain similar: Black will play a quick ...e5 to pressurize d4. If White has a bishop on d3, then Black also threatens ...e4 forking it and the knight on f3. White will try to advance his centre pawns to free his bishops: c4, d5, and f3 followed by e4 are all possible. If Black can prevent White from achieving this, then he will enjoy the better game. There are several move orders to reach the Main Variation besides the one given above; 4.e3 0-0 5.Bd3 d5 6.a3 Bxc3+ 7.bxc3 dxc4 8.Bxc4 c5 9.Nf3 Nc6 10.0-0 is one worth noting, because White may try 9.Ne2 instead.

• 7...Nc6 8.a3 Bxc3 9.bxc3 Qc7 is the Khasin Variation, named after International Master Abram Khasin. 10.cxd5 exd5 is the usual continuation. White will try to build up a strong centre with f3 and e4, or he may play for a kingside attack with f3 and g4. Black will try to restrain White's centre as well as he can, ideally blockading it, before mobilising his queenside pawn majority.

• The Averbakh Variation (7...Nbd7) was popularized by Grandmasters Viacheslav Ragozin
  Viacheslav Ragozin
  Viacheslav Vasilyevich Ragozin was a Soviet chess Grandmaster, an International Arbiter of chess, and a World Correspondence Chess Champion. He was also a chess writer and editor.- Biography :...
  
   and Yuri Averbakh
  Yuri Averbakh
  Yuri Lvovich Averbakh is a Soviet and Russian chess player and author. He is currently the oldest living chess grandmaster.-Life and career:...
  
  . The idea is to exchange pawns on c4 and d4 and then bring the d7-knight to b6 and d5. The same knight may also move to f8 to defend the black king. This line has gone out of fashion since the 1960s due to GM Svetozar Gligorić
  Svetozar Gligoric
  Svetozar Gligorić is a Serbian chess grandmaster. He won the championship of Yugoslavia a record twelve times, and is considered the best player ever from Serbia...
  
  's gambit idea 8.cxd5 exd5 9.a3 Ba5 10.b4! cxb4 11.Nb5! with pressure along the queenside files and a potential square for the knight on d6.

4...0-0: lines with Ne2

In general, the main line of the Rubinstein has held up very well for Black, so since the 1980s White has begun to look elsewhere for chances of obtaining an advantage. In the Rubinstein, White has often resorted to playing Ne2 rather than Nf3 at some point to be able to recapture on c3 with the knight, thus avoiding the doubled pawns. Two lines where White does this (following 4.e3 0-0) are:

5.Ne2 (Reshevsky Variation)

5.Bd3 d5 6.Ne2 (Modern Variation)

• The Reshevsky Variation was a specialty of GM Samuel Reshevsky
  Samuel Reshevsky
  Samuel "Sammy" Herman Reshevsky was a famous chess prodigy and later a leading American chess Grandmaster...
  
  . White will first play a3 to kick the bishop away, before moving his knight on e2 to a more active square. The main line runs 5.Ne2 d5 6.a3 Be7 7.cxd5, when both 7...exd5 and 7...Nxd5 are possible, the latter move leading to livelier play. GM Mikhail Gurevich
  Mikhail Gurevich (chess player)
  Mikhail Naumovich Gurevich is a Soviet chess player. He lived in Belgium from 1991 to 2005 and since then resides in Turkey....
  
   is currently the foremost expert in the Reshevsky Variation.

• 5.Bd3 d5 6.Ne2 and the closely related variant 5.Bd3 d5 6.cxd5 exd5 7.Ne2 were collectively dubbed the "Modern Variation" by FM Carsten Hansen in his book on the Rubinstein Nimzo-Indian. White again avoids the doubled pawns, but develops his bishop to d3 first so that it isn't blocked in by the knight on e2. Black usually continues 6...c5, putting more pressure on White's centre. While 7.a3 and 7.0-0 are playable, the main line is 7.cxd5 cxd4 8.exd4 Nxd5 9.0-0 Nc6, leading to an IQP position with White's knight on e2 rather than f3, as is normally the case. This gives Black the possibility of playing ...e5 at some point to completely liquidate the centre, although the resulting positions are rather drawish. White's main options on his tenth move are 10.a3, putting the question to the bishop, and 10.Bc2, intending 11.Qd3 with an attack on h7.

4...c5

Black puts pressure on d4 and leaves open the option of playing ...d5, or ...d6 and ...e5. The game can still transpose to the main line mentioned above after moves such as 5.Bd3 d5 6.Nf3 0-0 7.0-0, but there are two major variations particular to 4...c5:

• 5.Bd3 Nc6 6.Nf3 (6.Ne2 will likely transpose to the Modern Variation) 6...Bxc3+ 7.bxc3 d6 is the Hübner Variation, popularized by GM Robert Hübner
  Robert Hübner
  Robert Hübner is a respected German chess Grandmaster, chess writer, and papyrologist . At eighteen, he was joint winner of the West German Chess Championship...
  
   in the late 1960s and '70s and utilised by Bobby Fischer
  Bobby Fischer
  Robert James "Bobby" Fischer was an American chess Grandmaster and the 11th World Chess Champion. He is widely considered one of the greatest chess players of all time. Fischer was also a best-selling chess author...
  
   in his world championship match with Boris Spassky
  Boris Spassky
  Boris Vasilievich Spassky is a Soviet-French chess grandmaster. He was the tenth World Chess Champion, holding the title from late 1969 to 1972...
  
   in 1972 with great effect in game 5. It is slightly unusual in that Black captures on c3 without waiting for White to play a3, but this is because Black intends to immediately set up a blockade on the dark squares with ...d6 and ...e5. This is feasible because White's knight is on f3; if it were on e2 (as in some lines of the Sämisch), White could quickly advance his kingside pawns, but in the current line the knight must be moved away first. By closing the position, Black is able to make his knights superior to White's bishops, and the doubled c-pawns deprive White of any pawn breaks on the queenside. It was the success of this variation that motivated the current tendency for White players to choose lines where the doubled pawns are avoided. When he does play into this line, White has two main setups to choose from: he may immediately close the centre by playing 8.e4 e5 9.d5 Ne7, or play more flexibly with 8.0-0 e5 9.Nd2 0-0, but Black has full equality in both lines.

• 5.Ne2 the Rubinstein Variation (this is why 4.e3 is properly referred to as the Rubinstein "system" or "complex" to avoid confusion) is similar in spirit to the Reshevsky Variation: White prevents Black from doubling his pawns. After 5.Ne2, Black opens a path of retreat for his bishop with 5...cxd4 6.exd4, and now chooses between 6...d5 and 6...0-0. 6...d5 allows 7.c5, a typical continuation being 7...Ne4 8.Bd2 Nxd2 9.Qxd2 a5 10.a3 Bxc3 11.Nxc3 a4. White's c4-c5 push created a queenside pawn majority, which Black neutralized by playing ...a7-a5-a4. Black will now try to destroy the rest of White's pawn formation by playing ...b6 or ...e5, while White will try to use his lead in development to create attacking chances on the kingside. The alternative is 6...0-0 7.a3 Be7. Here Kasparov played 8.d5 exd5 9.cxd5 a few times early in his career, increasing his space advantage further but falling behind in development. A safer move for White is 8.Nf4.

4...b6

Favoured by Nimzowitsch, 4...b6 is a move in accordance with the spirit of the Nimzo-Indian: Black fianchetto

Fianchetto

In chess the fianchetto is a pattern of development wherein a bishop is developed to the second rank of the adjacent knight file, the knight pawn having been moved one or two squares forward....

es his light-squared bishop to increase his control over e4. White usually continues 5.Ne2, avoiding the doubled pawns, or 5.Bd3, continuing his development (5.Nf3 usually transposes to 5.Bd3). The main variations emerging from this move are:

5.Nge2 Ba6 (Fischer Variation)

5.Nge2 c5 (Romanishin-Psakhis Variation)

5.Nge2 Ne4 (American Variation)

5.Nge2 Bb7

5.Bd3 Bb7 6.Nf3 0-0 7.0-0 d5 (Classical Fianchetto Variation or Tal Variation)

5.Bd3 Bb7 6.Nf3 0-0 7.0-0 c5 (Keres Variation)

5.Bd3 Bb7 6.Nf3 Ne4 (Dutch Variation)

• The Fischer Variation (5.Ne2 Ba6) aims to exchange light-squared bishops after ...d5 so that Black can play on the light squares. Keres, Bronstein and Smyslov were early contributors to the theory of this line, and Fischer
  Bobby Fischer
  Robert James "Bobby" Fischer was an American chess Grandmaster and the 11th World Chess Champion. He is widely considered one of the greatest chess players of all time. Fischer was also a best-selling chess author...
  
   used it several times successfully. White may play 6.a3, which was favoured by Botvinnik
  Mikhail Botvinnik
  Mikhail Moiseyevich Botvinnik, Ph.D. was a Soviet and Russian International Grandmaster and three-time World Chess Champion. Working as an electrical engineer and computer scientist at the same time, he was one of the very few famous chess players who achieved distinction in another career while...
  
   and asks the bishop on b4 to clarify its intentions, or 6.Ng3, which was invented by Reshevsky and prepares e4.

• 5.Ne2 c5 6.a3 Ba5!? was dubbed the Romanishin-Psakhis Variation by Carsten Hansen because Oleg Romanishin
  Oleg Romanishin
  Oleg Mikhailovich Romanishin is a Ukrainian chess grandmaster and former European junior champion.Many honours and awards were bestowed on him as a young man. After winning the European Junior Championship in 1973, he became an International Master the same year...
  
   and Lev Psakhis
  Lev Psakhis
  Lev Borisovich Psakhis is a naturalised Israeli chess grandmaster, trainer and author. Born in Siberia, he is also a two-time former champion of the Soviet Union.-Biography:...
  
   were the two grandmasters who were primarily responsible for reviving the line and infusing it with new ideas. It can also arise via the move order 4.e3 c5 5.Ne2 b6 6.a3 Ba5. Black dares White to try and trap the bishop on a5, a challenge White usually takes up, but rarely successfully.

• The "American Variation" is another name invented by Hansen for the line 5.Ne2 Ne4, as it was pioneered by GM Isaac Kashdan
  Isaac Kashdan
  Isaac Kashdan was an American chess grandmaster and chess writer. Kashdan was one of the world's best players in the late 1920s and early 1930s. He was twice U.S. Open champion...
  
   and then developed by GM Bisguier
  Arthur Bisguier
  Arthur Bernard Bisguier is an American chess Grandmaster, chess promoter, and writer. Bisguier won two U.S. Junior Championships , three U.S. Open Chess Championship titles , and the 1954 United States Chess Championship title. He played for the United States in five chess Olympiads...
  
  , IM Anthony Santasiere
  Anthony Santasiere
  Anthony Edward Santasiere was an American chess master. Santasiere was a high school mathematics teacher by profession. His hobbies included creative writing and oil painting.-Chess career:...
  
   and currently GM Nick de Firmian
  Nick de Firmian
  Nicholas Ernest de Firmian , is a chess grandmaster and three-time U.S. chess champion, winning in 1987 , 1995, and 1998. He also tied for first in 2002, but Larry Christiansen won the playoff...
  
  . Black will exchange off two minor pieces and play ...f5 to keep e4 under control.

• 5.Ne2 Bb7 is a rather passive line: White seems to obtain a slight advantage by continuing 6.a3 Be7 7.d5, blocking in the bishop on b7 and making e3-e4 possible.

• The Classical Fianchetto Variation, also known as the Tal
  Mikhail Tal
  Mikhail Tal was a Soviet–Latvian chess player, a Grandmaster, and the eighth World Chess Champion.Widely regarded as a creative genius, and the best attacking player of all time, he played a daring, combinatorial style. His play was known above all for improvisation and unpredictability....
  
   Variation, can be reached through two move orders: 4.e3 b6 5.Bd3 Bb7 6.Nf3 0-0 7.0-0 d5 or 4.e3 0-0 5.Bd3 d5 6.Nf3 b6 7.0-0 Bb7. It is a solid variation where White often holds the initiative early on, but Black usually equalises in the end. White has two ways to attack Black's setup. The first is to play 8.cxd5 exd5 9.Ne5 followed by 10.f4 and transferring the queen or f1-rook to h3 via f3. This formation, known as the Pillsbury
  Harry Nelson Pillsbury
  Harry Nelson Pillsbury , was a leading chess player. At age 22, he won one of the strongest tournaments of the time , but his illness and early death prevented him from challenging for the World Chess Championship.- Early life :Pillsbury was born in Somerville, Massachusetts, moved to New York City...
  
   Attack, blocks in the dark-squared bishop and appears rather crude, but is actually quite dangerous. Black must create immediate pressure on White's centre by playing ...c5, and ...Ne4 may be a handy move at some point to block the b1-h7 diagonal and perhaps exchange some pieces. The main alternative for White is 8.a3 Bd6 9.cxd5 exd5 10.b4, which gains space on the queenside and makes it harder for Black to free his position with ...c5.

• The Keres Variation, characterised by the moves 5.Bd3 Bb7 6.Nf3 0-0 7.0-0 c5, is named after Estonian GM Paul Keres
  Paul Keres
  Paul Keres , was an Estonian chess grandmaster, and a renowned chess writer. He was among the world's top players from the mid-1930s to the mid-1960s....
  
  , although Smyslov and Bronstein were also early practitioners of this line. If allowed, Black will play ...cxd4 and ...d5 in the hope of leaving White with an isolated queen's pawn. Nowadays, White's most testing continuation is reckoned to be 8.Na4, ducking the exchange on c3 and threatening 9.a3. The knight will often stay on a4 for quite some time to assist in a potential c4-c5 push. After 8...cxd4 9.exd4, Black often sets up a Hedgehog
  Hedgehog Defence
  In chess, the Hedgehog is a pawn formation adopted usually by Black that can arise from several openings. Black exchanges his pawn on c5 for White's pawn on d4, and then places pawns on squares a6, b6, d6, and e6. These pawns form a row of "spines" behind which Black develops his forces...
  
   formation (pawns on a6, b6, d6 and e6), while White will try to pursue a strategy of gaining queenside space with b4 and c5.

• The Dutch Variation is so-called because after 5.Bd3 Bb7 6.Nf3 Ne4, Black usually follows up with 7...f5, with a position that resembles the Dutch Defence
  Dutch Defence
  The Dutch Defence is a chess opening characterised by the moves:-History:Elias Stein , an Alsatian who settled in The Hague, recommended the defence as the best reply to 1.d4 in his 1789 book Nouvel essai sur le jeu des échecs, avec des réflexions militaires relatives à ce jeu.-Theory:Black's 1.....
  
   (1.d4 f5). It is not a very common line, probably because White obtains good chances by playing 7.0-0 f5 8.d5, sacrificing a pawn to open up lines for his bishops.

Classical Variation (or Capablanca Variation) 4.Qc2

The Classical or Capablanca

José Raúl Capablanca

José Raúl Capablanca y Graupera was a Cuban chess player who was world chess champion from 1921 to 1927. One of the greatest players of all time, he was renowned for his exceptional endgame skill and speed of play...

 Variation was popular in the early days of the Nimzo-Indian, and though eventually superseded by 4.e3 it was revived in the 1990s; it is now just as popular as the Rubinstein. White aims to acquire the two bishops without compromising his pawn structure. The drawback is that the queen will move at least twice within the opening moves and that White's kingside development is delayed. Thus, even though White possesses the bishop pair, it is usually advisable for Black to open the game quickly to exploit his lead in development. Black has four common replies to 4.Qc2, these being 4...0-0, 4...c5, 4...d5, and 4...Nc6 (4...d6 intending ...Nbd7 and ...e5 is a rarer fifth option).

• 4...0-0 5.a3 Bxc3+ 6.Qxc3 b6 7.Bg5 is nowadays the main line of the Classical Variation (although 6...b5!? is an interesting gambit invented by Alvis Vitolinš
  Alvis Vitolinš
  Alvis Vītoliņš was a Latvian chess master.Awarded the International Master title in 1980, he was Latvian Champion in 1973 , 1976, 1977, 1978, 1982, 1983 and 1985...
  
  ). Black's usual choice is 7...Bb7, but 7...Ba6 is also possible to target the c-pawn, and 7...h6 8.Bh4 c5 and 7...c5 are sometimes played as well. After 7...Bb7, White's most straightforward move is 8.f3 preparing e4, but Black can counter with 8...h6 9.Bh4 d5, when the pawn grab 10.cxd5 exd5 11.Bxf6 Qxf6 12.Qxc7 Ba6 is very dangerous for White because of Black's better development. Therefore, White has sometimes tried 8.e3 instead, when after 8...h6 9.Bh4 d5?! 10.cxd5 exd5? 11.Bxf6 Qxf6 12.Qxc7 Ba6 White has 13.Bxa6 Nxa6 14.Qb7. Thus Black should prefer 8.e3 d6, planning ...Nbd7 and ...c5.
  Both players can deviate from the main line. Instead of 7.Bg5, White can play 7.Nf3 Bb7 8.e3, intending to develop the dark-squared bishop to b2. Another possibility is 4.Qc2 0-0 5.e4, although this is somewhat inconsistent with 4.Qc2 as Black might be able to double White's c-pawns at some point (the queen must guard e4), something 4.Qc2 was supposed to prevent. After 5.a3 Bxc3+ 6.Qxc3, Black can also try 6...Ne4 7.Qc2 f5, which is similar to the Dutch Variation (see 4.e3 b6), but without the doubled pawns for White.

• 4...c5 exploits the fact that on c2, the queen no longer defends the d-pawn. If White defends the pawn, then Black gets an easy game by keeping the pressure on d4, so White almost always plays 5.dxc5. Black can choose to recapture on c5 with the bishop (e.g. 5...Bxc5 or 5...0-0 6.a3 Bxc5), or with the knight (after 5...Na6 or 5...0-0 6.Nf3 Na6). In the former case, the bishop will eventually retreat to e7 and Black will set up a Hedgehog
  Hedgehog Defence
  In chess, the Hedgehog is a pawn formation adopted usually by Black that can arise from several openings. Black exchanges his pawn on c5 for White's pawn on d4, and then places pawns on squares a6, b6, d6, and e6. These pawns form a row of "spines" behind which Black develops his forces...
  
   formation (pawns on a6, b6, d6 and e6). If Black recaptures with the knight, he will often have to give up the bishop pair at some point with ...Bxc3, but the knight is useful on c5 and can later go to e4, attacking the queen on c3. 4...c5 5.dxc5 0-0 (the Pirc Variation) was one of the reasons why 4.Qc2 was not popular during the mid-20th century, because the lines where Black eventually recaptures with the knight was reckoned to give Black easy equality, while the line which prevented this maneuver, 6.a3 Bxc5 7.Nf3 Nc6 8.Bg5 Nd4 9.Nxd4 Bxd4 10.e3 Qa5 11.exd4 Qxg5, left the Black queen active, while White still needs to secure the king. It was the discovery of 12.Qd2! which revived this line for White, because the endgame after 12...Qxd2+ 13.Kxd2 offers White a slight edge. Indeed, Edmar Mednis
  Edmar Mednis
  Edmar John Mednis was an American International Grandmaster of chess born in Riga, Latvia. He was also a popular and respected chess writer.-Biography:...
  
  's remark was that the entire Pirc Variation had become unplayable at the highest level, while Modern Chess Openings
  Modern Chess Openings
  Modern Chess Openings is an important reference book on the chess openings, first published in 1911 by the British players Richard Clewin Griffith and John Herbert White...
  
   (MCO) cites this variation as the main problem with 4...c5. However, players like Kramnik have been willing to defend the Black side of this line against players like Kasparov.

• 4...d5 is another move that strikes immediately in the centre, and was a favourite of Mikhail Botvinnik
  Mikhail Botvinnik
  Mikhail Moiseyevich Botvinnik, Ph.D. was a Soviet and Russian International Grandmaster and three-time World Chess Champion. Working as an electrical engineer and computer scientist at the same time, he was one of the very few famous chess players who achieved distinction in another career while...
  
  . After 5.cxd5, Black can either recapture with the queen or pawn. 5...Qxd5 is the Romanishin
  Oleg Romanishin
  Oleg Mikhailovich Romanishin is a Ukrainian chess grandmaster and former European junior champion.Many honours and awards were bestowed on him as a young man. After winning the European Junior Championship in 1973, he became an International Master the same year...
  
   System: the idea is that after 6.Nf3 Qf5 7.Qxf5 exf5, Black strengthens his grip on e4 and makes e6 available for the bishop, which is enough for him to obtain equality. White can avoid this with 6.e3 so that 6...Qf5 can be met with 7.Bd3, but the e3-pawn blocks in White's c1-bishop. The older alternative is 5...exd5 6.Bg5 h6, which tends to be a rather sharp line. After 4...d5, White can also play 5.a3 Bxc3+ 6.Qxc3 Ne4 7.Qc2, when Black may play 7...c5 or 7...Nc6 intending ...e5. Even though White possesses the pair of bishops, Black still strives for a quick opening of the position to exploit his lead in development. The usual result of this is a dynamically balanced position.

• 4...Nc6 is the Zürich
  Zürich
  Zurich is the largest city in Switzerland and the capital of the canton of Zurich. It is located in central Switzerland at the northwestern tip of Lake Zurich...
  
  or Milner-Barry Variation (named after British chess player Stuart Milner-Barry
  Stuart Milner-Barry
  Sir Stuart Milner-Barry KCVO, CB, OBE was a British chess player, chess writer, World War II codebreaker and civil servant. He represented England in chess both before and after World War II...
  
  ). Black gives up the dark-squared bishop, but places his central pawns on d6 and e5 so that his remaining bishop is unimpeded. To avoid moving his queen, White will play Bd2 at some point so that when Black takes the knight, White can recapture with the bishop. 4...Nc6 is out of fashion because most players prefer to avoid blocking their c-pawn. A topical line would go 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Qc2 Nc6 5.Nf3 (better than 5.e3) d6, with the idea of playing e5. Black often prepares this with castling and ...Re8 or by playing Qe7. After Black plays ...e5, White usually responds with d5. Black is willing to lose a tempo moving the Knight back to b8 (or e7, which is often better) because the position is closed. White usually plays on the Queenside in this variation, while Black will try to play on the Kingside with ...f5 and possibly transferring the c6 Knight over to the Kingside after White's d5. Today, the line arises quite often by transposition from the Black Knights Tango, e.g. 1.d4 Nf6 2.c4 Nc6 3.Nf3 e6 4.Nc3 Bb4 5.Qc2.

Kasparov Variation 4.Nf3

4.Nf3 is known as the Kasparov Variation, since Garry Kasparov

Garry Kasparov

Garry Kimovich Kasparov is a Russian chess grandmaster, a former World Chess Champion, writer, political activist, and one of the greatest chess players of all time....

 used it to great effect against Anatoly Karpov

Anatoly Karpov

Anatoly Yevgenyevich Karpov is a Russian chess grandmaster and former World Champion. He was the official world champion from 1975 to 1985 when he was defeated by Garry Kasparov. He played three matches against Kasparov for the title from 1986 to 1990, before becoming FIDE World Champion once...

 in their 1985 World Championship match. Kasparov played 4.Nf3 six times, scoring three wins and three draws. Today as White, this is a favourite weapon of GM Alexei Barsov

Alexei Barsov

Alexei Barsov is an Uzbekistani chess Grandmaster.- Chess career :Barsov, lawyer by education, has been a professional chess player since the early 1990s, and is one of the premier players in Uzbekistan. For some years he was the coach of the world chess champion Rustam Kasimdzhanov.He won the...

 and former Women's Champion Nona Gaprindashvili

Nona Gaprindashvili

Nona Gaprindashvili is a Georgian chess player, the sixth women's world chess champion , and first female Grandmaster. Born in Zugdidi, Georgia , she was the strongest female player of her generation....

.

White develops the knight to a natural square and waits to see Black's reply. 4...d5 transposes to the Ragozin Defence of the Queen's Gambit Declined and 4...b6 5.Bg5 Bb7 transposes to the Nimzo/Queen's Indian hybrid line, so 4...c5 is the most common move that stays within Nimzo-Indian territory. Now 5.e3 transposes to the Rubinstein System, but the main move is 5.g3, which leads to a position that also arises from the Fianchetto Variation. 5.g3 cxd4 6.Nxd4 0-0 7.Bg2 d5 8.cxd5 Nxd5 can be considered the main line. Black has dissolved White's centre, but the bishop on g2 exerts pressure on the black queenside, which White may augment with 9.Qb3.

This line can also arise from the Bogo-Indian Defence

Bogo-Indian Defence

The Bogo-Indian Defence is a chess opening characterised by the moves:-Variations:White has three viable moves to meet the check. 4.Nc3 is a transposition to the Kasparov Variation of the Nimzo-Indian, therefore the main independent variations are 4.Bd2 and 4.Nbd2.-4...

 (1.d4 Nf6 2.c4 e6 3.Nf3 Bb4+) if White blocks the check with 4.Nc3. Most Bogo-Indian players are also Nimzo-Indian players, but for those who are not, this transposition into the Nimzo is something they need to be prepared for.

Other variations

• 4. f3 - This line has no generally accepted name, so is usually just referred to as the 4.f3 Variation. It has previously been called the Gheorghiu Variation (a name given by Gligoric),who often played it early in his career, even defeating Fischer, and sometimes the Shirov Variation, after Alexei Shirov
  Alexei Shirov
  Alexei Dmitrievich Shirov is a Soviet-born Latvian chess grandmaster. He has consistently ranked among the world's top players since the early 1990s, and reached a ranking as high as number four in 1998...
  
   who used it with great success in the early 1990s, before he lost three consecutive games with the line and abandoned it. According to chess365.com it is called the Kmoch Variation. It is a straightforward attempt to seize control of e4, though at the cost of delaying development, and therefore attempts to refute Black's plan, which has been to play for control of the e4-square. Black's most common reply is 4...d5 5.a3 Bxc3+ 6.bxc3 c5 7.cxd5 Nxd5, a position also reached from the Sämisch Variation. Black's pressure on c3 and d4 compels White to play 8.dxc5, trying to open the position for his two bishops. White will follow up with e4, and Black will counter with ...e5 at some point to prevent White from pushing his e- and f-pawns further up the board. Another approach for Black is to play 4...c5, after which White plays 5.d5 to keep his central pawns together reaches a Benoni-style position, and Black's main replies are 5...b5, 5...0-0, 5...Bxc3+ and 5...Nh5. 5.a3 Bxc3+ 6.bxc3 is a direct transposition to the Saemisch Variation below.

• 4. Bg5 - The Leningrad Variation received its name because its theory was developed extensively by players from that city, such as Boris Spassky
  Boris Spassky
  Boris Vasilievich Spassky is a Soviet-French chess grandmaster. He was the tenth World Chess Champion, holding the title from late 1969 to 1972...
  
  . The main line runs 4. ... h6 5. Bh4 c5 6. d5 d6 7. e3 Bxc3+ 8. bxc3 e5, when Black has achieved a Hübner Variation-like blockade, the difference being that White's dark-squared bishop is outside the pawn chain. The pin on the f6-knight is very annoying, and Black often finds himself compelled to break it by playing the drastic ...g7-g5, which also clamps down on a potential f2-f4 break by White. This move weakens Black's kingside, so he often will not castle, walking his king to c7 via d8. An interesting alternative to 6....d6 is ....b5, much played in the 1970s after Mikhail Tal
  Mikhail Tal
  Mikhail Tal was a Soviet–Latvian chess player, a Grandmaster, and the eighth World Chess Champion.Widely regarded as a creative genius, and the best attacking player of all time, he played a daring, combinatorial style. His play was known above all for improvisation and unpredictability....
  
   scored a crushing win over Spassky at Tallinn
  Tallinn
  Tallinn is the capital and largest city of Estonia. It occupies an area of with a population of 414,940. It is situated on the northern coast of the country, on the banks of the Gulf of Finland, south of Helsinki, east of Stockholm and west of Saint Petersburg. Tallinn's Old Town is in the list...
  
   1973.

• 4.a3 - The Sämisch Variation (named after Fritz Sämisch
  Friedrich Sämisch
  Friedrich Sämisch was a German chess grandmaster .-Main results:* 2nd at Berlin 1920...
  
  ) is a direct attempt to refute Black's strategic concept, as White gives up a tempo and concedes doubled c-pawns to gain the bishop pair. After 4...Bxc3+ 5.bxc3, Black has several possibilities, the most common of which is that he immediately begins to blockade the doubled pawns with 5....c5 and applies more pressure on the (often doomed) pawn at c4 with the moves ...Ba6, ...Nc6-a5 and ...Rc8. In the early days of this line, 5....d5 was frequently played, though it was soon realised that this enabled White to liquidate the weakness at c4, so the idea fell from favour, particularly after the game Botvinnik-Capablanca, AVRO 1938, and has never been revived at top level. As compensation, White establishes a powerful centre, in order to play for a kingside attack before Black can make use of his static advantages. White has two main options for playing: he can move slowly into the centre with 6.e3, or he can play 6.f3, followed by 7.e4 to take a quick hold in the centre. In practice, however, Black has demonstrated that White's structural weaknesses are more serious than the attacking chances he gets, so this variation is rarely seen nowadays. The Sämisch Variation was employed five times by Mikhail Botvinnik
  Mikhail Botvinnik
  Mikhail Moiseyevich Botvinnik, Ph.D. was a Soviet and Russian International Grandmaster and three-time World Chess Champion. Working as an electrical engineer and computer scientist at the same time, he was one of the very few famous chess players who achieved distinction in another career while...
  
   against Tal
  Mikhail Tal
  Mikhail Tal was a Soviet–Latvian chess player, a Grandmaster, and the eighth World Chess Champion.Widely regarded as a creative genius, and the best attacking player of all time, he played a daring, combinatorial style. His play was known above all for improvisation and unpredictability....
  
   in the 1960 World Chess Championship
  World Chess Championship 1960
  The 1960 World Chess Championship was played between Mikhail Botvinnik and Mikhail Tal in Moscow from March 15 to May 7, 1960. Tal won.- 1958 Interzonal Tournament:An interzonal chess tournament was held in Portorož in 1958.-1959 Candidates Tournament:...
  
  , with five draws resulting, and once in the 1961 rematch
  World Chess Championship 1961
  The 1961 World Chess Championship was played between former champion Mikhail Botvinnik and champion Mikhail Tal in Moscow from March 15 to May 13, 1961. Tal had unseated Botvinnik in the 1960 match, thus Botvinnik was entitled to this rematch the next year. Botvinnik, a Russian, defeated Latvian...
  
  , with a win for White.

• 4. g3 - The Fianchetto Variation resembles the Catalan System, where White fianchetto
  Fianchetto
  In chess the fianchetto is a pattern of development wherein a bishop is developed to the second rank of the adjacent knight file, the knight pawn having been moved one or two squares forward....
  
  es his king's bishop to put pressure on the centre squares from the flank. Black can play 4...c5 5.Nf3 with a position also reached from the Kasparov Variation (see above), but 4...d5 is possible as well. This is considered the strongest response, since if allowed, Black can take the pawn on c4 and often keep it. This is not usually possible in the Catalan, where White's knight is developed to d2 and can simply recapture on c4.

• 4. Qb3 - The Spielmann Variation is named after Rudolf Spielmann
  Rudolf Spielmann
  Rudolf Spielmann was an Austrian-Jewish chess player of the romantic school, and chess writer.-Career:He was a lawyer but never worked as one....
  
   who played it at Carlsbad, 1929, and was played at GM level in the early 1930s, though soon eclipsed in popularity by 4.Qc2. Like the Classical Variation, it avoids the doubling of White's pawns. However, unlike 4.Qc2, the queen has no control over e4, which Black can exploit by playing 4...c5 5.dxc5 Nc6 6.Nf3 Ne4, for example. Thus, despite the occasional revival by GMs Vladimir Akopian, Vladimir Malaniuk
  Vladimir Malaniuk
  Vladimir Pavlovich Malaniuk is a Ukrainian chess Grandmaster....
  
   and Jeroen Piket
  Jeroen Piket
  Jeroen Piket is a retired Dutch chess player who earned the Grandmaster title in 1989. He won the Dutch Chess Championship in 1990, 1991, 1992, and 1994. Other notable results include a second place at the Hoogovens tournament 1997...
  
  , this variation is also unusual.

• 4. e4 - The Dilworth Gambit, named for Vernon Dilworth, who contributed an article on the variation to the March 1949 issue of CHESS magazine
  CHESS magazine
  CHESS magazine , also called CHESS and previously called CHESS Monthly, is a chess magazine published monthly in the UK by Chess and Bridge Limited. CHESS was founded by Baruch Harold Wood in 1935 in Sutton Coldfield. Wood edited it until 1988, when it was taken over by Pergamon Press and changed...
  
  . Dilworth's idea was 4...Nxe4 5.Qg4 Nxc3 6.Bd2. However, White's compensation for the pawn is nebulous at best, and the line accordingly never developed a following beyond Dilworth himself. http://www.chesshistory.com/winter/winter10.html (No. 3762) Chris Ward
  Chris Ward (chess player)
  Chris G Ward is a British chess Grandmaster , chess coach, and author. He won the British Championship in 1996, earning the GM title in the process. He is the author of two well-received books on a variation of the Sicilian Defence known as the Dragon Variation, in addition to a number of other...
  
   called the gambit "critical, but basically rubbish".

• 4. Bd2, unpinning the knight, is a move which is common among amateurs who have no theoretical knowledge when they face the Nimzo-Indian. Although the move is not bad, it is unambitious. The strategic aim of obtaining the bishop pair without conceding the doubled pawns fails, for after e.g., 4...Bxc3 5.Bxc3 Ne4, White does not get to keep both bishops, and fair trades are usually not in White's interests since White has an advantage in space.

• 4. Qd3 - The Mikenas Variation is named after Vladas Mikėnas
  Vladas Mikenas
  Vladas Mikėnas was a Lithuanian International Master of chess, an Honorary Grandmaster, and a journalist.- Early life :Vladas Mikėnas played for Lithuania at first board in five official and one unofficial Chess Olympiads....
  
  . That supports the knight, and brings the queen to a central location, but the queen is exposed on d3, making this variation rare.

ECO codes

In the Encyclopaedia of Chess Openings

Encyclopaedia of Chess Openings

The Encyclopaedia of Chess Openings is a classification system for the opening moves in a game of chess. It is presented as a five volume book collection describing chess openings...

, the Nimzo-Indian Defence has codes E20 to E59. All codes begin with 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4, excluding E20, which also includes alternatives to 3...Bb4 apart from 3...d5 (which would be the Queen's Gambit Declined

Queen's Gambit Declined

The Queen's Gambit Declined is a chess opening in which Black declines a pawn offered by White in the Queen's Gambit:This is known as the Orthodox Line of the Queen's Gambit Declined...

).

E20 - 1.d4 Nf6 2.c4 e6 3.Nc3 (includes Romanishin Variation, 4.f3 Variation of Nimzo-Indian excluding 4.f3 d5 5.a3 Bxc3+, which is covered under E25)

E21 - 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.Nf3 (Kasparov Variation excluding 4...c5 5.g3, which is covered under E20)

E22 - 4.Qb3 (E22 and E23 cover the Spielmann Variation)

E23 - 4.Qb3 c5

E24 - 4.a3 (E24-E29 cover the Sämisch Variation)

E25 - 4.a3 Bxc3+ 5.bxc3 c5

E26 - 4.a3 Bxc3+ 5.bxc3 c5 6.e3

E27 - 4.a3 Bxc3+ 5.bxc3 0-0

E28 - 4.a3 Bxc3+ 5.bxc3 0-0 6.e3

E29 - 4.a3 Bxc3+ 5.bxc3 0-0 6.e3 c5

E30 - 4.Bg5 (E30 and E31 cover the Leningrad Variation)

E31 - 4.Bg5 h6 6.Bh4 c5 6.d5 d6

E32 - 4.Qc2 (includes 4...0-0; E32-E39 cover the Classical/Capablanca Variation)

E33 - 4.Qc2 Nc6 (Zürich/Milner-Barry Variation)

E34 - 4.Qc2 d5

E35 - 4.Qc2 d5 5.cxd5 exd5

E36 - 4.Qc2 d5 5.a3

E37 - 4.Qc2 d5 5.a3 Bxc3+ 6.Qxc3 Ne4

E38 - 4.Qc2 c5

E39 - 4.Qc2 c5 5.dxc5 0-0

E40 - 4.e3 (includes Taimanov Variation; E40-E59 cover the Rubinstein System)

E41 - 4.e3 c5 (includes Hübner Variation)

E42 - 4.e3 c5 5.Ne2 (Rubinstein Variation, Romanishin-Psakhis Variation via 5...b6 6.a3 Ba5)

E43 - 4.e3 b6 (includes Dutch Variation, Keres Variation)

E44 - 4.e3 b6 5.Ne2 (includes American Variation, 5...Bb7 Variation)

E45 - 4.e3 b6 5.Ne2 Ba6 (Fischer Variation)

E46 - 4.e3 0-0 (includes Reshevsky Variation)

E47 - 4.e3 0-0 5.Bd3

E48 - 4.e3 0-0 5.Bd3 d5 (includes Modern Variation)

E49 - 4.e3 0-0 5.Bd3 d5 6.a3

E50 - 4.e3 0-0 5.Nf3

E51 - 4.e3 0-0 5.Nf3 d5

E52 - 4.e3 0-0 5.Nf3 d5 6.Bd3 b6 (Classical Fianchetto/Tal Variation)

E53 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 (includes Averbakh Variation)

E54 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 7.0-0 dxc4 8.Bxc4 (includes Karpov Variation, Bronstein Variation, Smyslov Variation)

E55 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 7.0-0 dxc4 8.Bxc4 Nbd7 (Parma Variation)

E56 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 7.0-0 Nc6 (includes Larsen Variation)

E57 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 7.0-0 Nc6 8.a3 dxc4 9.Bxc4 cxd4

E58 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 7.0-0 Nc6 8.a3 Bxc3 9.bxc3 (includes Khasin Variation)

E59 - 4.e3 0-0 5.Nf3 d5 6.Bd3 c5 7.0-0 Nc6 8.a3 Bxc3 9.bxc3 dxc4 10.Bxc4 (includes Main Variation)

Further reading