Chess opening

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The starting position of chess

The opening is the initial stage of a chess game. It usually consists of established theory. The other phases are the middlegame and the endgame.^[1] Many opening sequences, known as openings, have standard names such as "Sicilian Defense". The Oxford Companion to Chess lists 1,327 named openings and variants, and there are many others with varying degrees of common usage.^[2]

Standard openings have a variety of aims, including developing rapidly, harmoniously, and actively, controlling the center, king safety, and certain other gameplay-related goals and psychological goals.

Opening moves that are considered standard are referred to as "book moves", or simply "book".^[3] When a game begins to deviate from known opening theory, the players are said to be "out of book".^[3] In some openings, book lines have been worked out for over 30 moves, such as some lines in the classical King's Indian Defense and in the Najdorf Variation of the Sicilian Defense.^[4] A new sequence of moves in the opening is referred to as a theoretical novelty. When kept secret until used in a competitive game, it is often known as a prepared variation, a powerful weapon in top-class competition.^[5]

Professional chess players spend years studying openings, and they continue doing so throughout their careers as opening theory continues to evolve. Players at the club level also study openings, but the importance of the opening phase is less there since games are rarely decided in the opening. The study of openings can become unbalanced if it is to the exclusion of tactical training and middlegame and endgame strategy.^[6]

Aims of the opening

Common aims in opening play

Whether they are trying to gain the upper hand as White, or to equalize as Black or to create dynamic imbalances, players generally devote a lot of attention in the opening stages to the following strategies:^[7]

Development: One of the main aims of the opening is to mobilize the pieces on useful squares where they will have impact on the game. To this end, knights are usually developed to f3, c3, f6, and c6 (or sometimes e2, d2, e7, or d7), and both players' king and queen pawns are moved so the bishops can be developed (alternatively, the bishops may be fianchettoed with a maneuver such as g3 and Bg2). Rapid mobilization is considered key. The queen, and to a lesser extent the rooks, are not usually played to a central position until later in the game, when many minor pieces and pawns are no longer present.^[8]
Control of the center: At the start of the game, it is not clear on which part of the board the pieces will be needed. Controlling the central squares, however, allows pieces to be moved to any part of the board relatively easily, and can also have a cramping effect on the opponent. The classical view is that central control is best effected by placing pawns there, ideally establishing pawns on d4 and e4 (or d5 and e5 for Black). However, the hypermodern school showed that it was not always necessary or even desirable to occupy the center in this way, and that too broad a pawn front could be attacked and destroyed, leaving its architect vulnerable; an impressive-looking pawn center is worth little unless it can be maintained. The hypermoderns instead advocated controlling the center from a distance with pieces, breaking down one's opponent's center, and only taking over the center oneself later in the game. This leads to openings such as Alekhine's Defense – in a line like 1.e4 Nf6 2.e5 Nd5 3.d4 d6 4.c4 Nb6 5.f4 (the Four Pawns Attack) White has a formidable pawn center for the moment, but Black hopes to undermine it later in the game, leaving White's position exposed.^[9]
King safety: The king is somewhat exposed in the middle of the board. Measures must be taken to reduce his vulnerability. It is therefore common for both players either to castle in the opening (simultaneously developing one of the rooks) or to otherwise bring the king to the side of the board via artificial castling.
Prevention of pawn weaknesses: Most openings strive to avoid the creation of pawn weaknesses such as isolated, doubled and backward pawns, pawn islands, etc. Some openings sacrifice endgame considerations for a quick attack on the opponent's position. Some unbalanced openings for Black, in particular, make use of this idea, such as the Dutch and the Sicilian. Other openings, such as the Alekhine and the Benoni, invite the opponent to overextend and form pawn weaknesses. Specific openings accept pawn weaknesses in exchange for compensation in the form of dynamic play. (See Pawn structure.)
Piece coordination: As the players mobilize their pieces, they both seek to ensure that they are working harmoniously towards the control of key squares.^[9]
Creating positions in which the player is more comfortable than the opponent: Transposition is one common way of doing this.^[10]

Apart from these ideas, other strategies used in the middlegame may also be carried out in the opening. These include preparing pawn breaks to create counterplay, creating weaknesses in the opponent's pawn structure, seizing control of key squares, making favorable exchanges of minor pieces (e.g. gaining the bishop pair), or gaining a space advantage, whether in the center or on the flanks.

Top-level objectives

At higher levels of competition, for many years the main objectives of opening play were to obtain a better position when playing as White and to equalize when playing as Black. The idea behind this is that playing first gives White a slight initial advantage; for example, White will be the first to attack if the game opens symmetrically (Black mirrors White's moves).^[7]

Since about the 1950s another objective has gradually become more dominant. According to IM Jeremy Silman, the purpose of the opening is to create dynamic imbalances between the two sides, which will determine the character of the middlegame and the strategic plans chosen by both sides.^[11] For example, in the main line of the Winawer Variation of the French Defense (1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.a3 Bxc3+ 6.bxc3), White will try to use their bishop pair and space advantage to mount an attack on Black's kingside, while Black will seek simplifying exchanges (in particular, trading off one of White's bishops to blunt this advantage) and counterattack against the weakened pawns on White's queenside; both players accept different combinations of advantages and disadvantages. This idea was a doctrine of the Soviet school of chess.

A third objective, which is complementary to the previous ones and has been common since the 19th century, is to lure the opponent into positions with which the player is more familiar and comfortable than the opponent. This is usually done by transpositions, in which a game that apparently starts with one opening can reach a position that is normally produced by a different opening.^[10]

Opening repertoires

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The Perenyi Attack (1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Be3 e6 7.g4), position after 7...e5 8.Nf5 g6 9.g5 gxf5 10.exf5 d5 11.Qf3 d4. This attack has been played several times between grandmasters, but chess author Lars Bo Hansen does not recommend this to amateurs.

Most players realize after a while that they play certain types of positions better than others, and that the amount of theory they can learn is limited. Therefore, most players specialize in certain openings where they know the theory and that lead to positions they favor.^[12] The set of openings a player has specialized in is called an opening repertoire.^[12] The main elements a player needs to consider in a repertoire are:

As White, whether to open with 1.e4, 1.d4, 1.c4, or 1.Nf3
As Black, a defense against any of these openings

A very narrow repertoire allows for deeper specialization but also makes a player less flexible to vary against different opponents. In addition, opponents may find it easier to prepare against a player with a narrow repertoire.^[13]

The main openings in a repertoire are usually reasonably sound; that is, they should lead to playable positions even against optimal counterplay. Unsound gambits are sometimes used as surprise weapons, but are unreliable for a stable repertoire. Repertoires often change as a player develops, and a player's advancement may be stifled if the opening repertoire does not evolve. Some openings that are effective against amateur players are less effective at the master level. For example, Black obtains active play in return for a pawn in the Benko Gambit; amateur players may have trouble defending against Black's activity, while masters are more skilled at defending and making use of the extra pawn. Some openings are so complex and theoretical that amateur players will have trouble understanding them. An example is the Perenyi Attack of the Sicilian Defense (see diagram), which yields an immensely complicated and tactical position which even strong players have difficulty handling, and which is beyond the comprehension of most amateurs.^[6]

Opening nomenclature

Major changes in the rules of chess in the late fifteenth century increased the speed of the game, consequently emphasizing the importance of opening study. Thus, early chess books, such as the 1497 text of Luis Ramirez de Lucena, present opening analysis, as do Pedro Damiano (1512) and Ruy López de Segura (1561). Ruy López's disagreement with Damiano regarding the merits of 2...Nc6 led to 3.Bb5 (after 1.e4 e5 2.Nf3 Nc6) being named for him as the Ruy Lopez or Spanish Opening.^[14] Opening theory was studied more scientifically from the 1840s on, and many opening variations were discovered and named in this period and later.

Opening nomenclature developed haphazardly, and most names are historical accidents not based on systematic principles. In the early 1930s, the nascent FIDE embarked on a project to standardize opening nomenclature, culminating in the publication of a short booklet in 1933, but this had little impact.^[15]

The oldest openings tend to be named for geographic places and people. Many openings are named after nationalities of players who advocated them, for example Indian, English, Spanish, French, Dutch, Scotch, Russian, Italian, Scandinavian and Sicilian, or places where important games featuring the opening were played such as Vienna, Berlin, and Wilkes-Barre.^[16] The Catalan System is named after the Catalonia region.

Chess players' names are the most common sources of opening names.^[16] The name given to an opening is not always that of the first player to adopt it; often an opening is named for the player who was the first to popularize it or to publish analysis of it. Eponymic openings include the Ruy Lopez, Alekhine's Defense, Morphy Defense, and the Réti Opening. Some opening names honor two people, such as the Caro–Kann and the Smith–Morra.

A few opening names are purely descriptive, such as Giuoco Piano (Italian: quiet game), Two Knights Defense, Four Knights Game and Bishop's Opening.

Some openings have been given fanciful names, often names of animals. This practice became more common in the 20th century. By then, most of the more common and traditional sequences of opening moves had already been named, so these tend to be unusual or recently developed openings like the Orangutan, Hippopotamus, Elephant, Hedgehog, and, most recently, the Cow. A few are given humorous names, such as the Monkey's Bum and the Toilet Variation.

Opening names usually include characterizing terms like "opening", "variation", "defense", "gambit", or "attack"; however, the terminology is inconsistent and imprecise, and is not a useful basis for classification.^[17] Broadly, these terms are used as follows:

Game: Used for some of the oldest named openings, such as the Scotch Game, Vienna Game, and Four Knights Game. In the 19th century it was used for other common openings such as the Sicilian Defense ("Sicilian Game") and French Defense ("French Game").
Opening: This usually refers to an opening played by White, such as the English Opening or Bird's Opening.
Defense: Refers to an opening chosen by Black, such as Two Knights Defense or Caro-Kann Defense. Some openings described as "defenses", such as the King's Indian Defense and Sicilian Defense, can in fact be quite aggressive.
Gambit: An opening that involves the sacrifice of material, usually one or more pawns. Most openings described as "Gambits" are played by White (e.g., King's Gambit), but a few are played by Black (e.g., Latvian Gambit, Stafford Gambit). The terms "Accepted" or "Declined" may be appended to the name, depending on whether the opponent takes the offered material, as in the Queen's Gambit Accepted and Queen's Gambit Declined. In the case of the Queen's Gambit, the sacrifice of material is only temporary as there is no good way for Black to keep the pawn (Ward 1999:10).
Countergambit: A gambit played by Black, often in response to another gambit. Examples of this include the Albin Countergambit in response to the Queen's Gambit, the Falkbeer Countergambit in response to the King's Gambit, and the Greco Counter Gambit (the former name of the Latvian Gambit) in response to the King's Knight Opening.
Variation: Used to describe a branch of another named opening, for example the Najdorf Variation, a line of the Sicilian Defense.
System: A method of development that can be used against many different setups by the opponent. Examples include London System, Colle System, Réti System, Barcza System, and Hedgehog System.
Attack: Usually used to describe an aggressive or provocative variation such as the Albin–Chatard Attack (or Chatard–Alekhine Attack), the Fried Liver Attack in the Two Knights Defense, and the Grob Attack. The King's Indian Attack is an exception, describing a King's Indian Defense with colors reversed.
Reversed, inverted: A Black opening played by White, or more rarely a White opening played by Black. Examples include the Sicilian Reversed (from the English Opening) and the Inverted Hungarian. The Reti, King's Indian Attack, Sicilian Reversed (from the English), and other "Black played by White with an extra tempo" often start with 1.Nf3 or 1.c4.^[18]
Anti-: Prefix for openings designed to avoid a specific line, for example the Anti-Marshall (against the Marshall (Counter) Attack in the Ruy Lopez) and the Anti-Meran Gambit (against the Meran Variation of the Semi-Slav Defense).

Classification of chess openings

White's most common first moves

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1.d4

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1.e4

Chess openings are primarily categorized by move sequences.^[19] In the initial position, White has twenty legal moves;^[20] of these, 1.e4 and 1.d4, followed by 1.Nf3 and 1.c4, are by far the most popular as they do the most to promote rapid development and control of the center. Likewise, Black has twenty legal responses to White's opening move.^[20]

Regardless of White's choice, among the four common first moves, symmetrical replies (e.g. 1.e4 e5 or 1.d4 d5) along with defenses beginning with 1...c6 and 1...e6, often followed by the center thrust 2...d5, are common. Defenses with an early ...d6 coupled with a kingside fianchetto are also common.

An important scheme for classifying chess openings for serious players is by ECO code, a series of 500 opening codes assigned by the Encyclopaedia of Chess Openings. Although these codes are valuable for the serious study of chess openings, they are not very practical for a broad survey of the chess opening as the codes obscure common structural features between related openings. Also, the codes were assigned decades ago, and have not changed.

Chess openings may be broadly classified into king’s pawn openings, queen’s pawn openings, flank openings, and irregular openings. Since these categories are still individually very large, it is common to break each of them down further, such as into symmetrical and asymmetrical replies. For example, the openings arising after the symmetrical 1.e4 e5 can be distinguished as the Open Games;^[21] 1...c5 is by far the most frequent of the asymmetrical replies to 1.e4, which are the so-called Semi-Open Games.^[22] Similarly, for 1.d4, 1...Nf6 is the most important^[23] and most frequent by far of the asymmetrical replies to 1.d4; it can lead to various Indian systems.

Open games: 1.e4 e5

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Open Game

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Ruy Lopez

1.e4, moving the king pawn two spaces forward, is the most popular opening move. Its strengths including controlling the center and activating two pieces, the queen and a bishop. Bobby Fischer famously called 1.e4 "Best by test." On the downside, 1.e4 places a pawn on an undefended square and weakens d4 and f4.

The Open Games result after Black mirrors White's move 1.e4 by replying with 1...e5.^[24] The oldest openings in chess follow 1.e4 e5. White's most popular reply to 1...e5 is 2.Nf3, attacking Black's e-pawn, preparing to castle, and supporting the advance of the queen's pawn to d4.

Black's most common reply to 2.Nf3 is 2...Nc6, which has continuations such as:

3.Bb5, the Ruy Lopez, which attacks the knight. It was first recorded in the 15th century.
3.Bc4, the Italian Game, which eyes the square f7, defended only by Black's king. The Evergreen Game featured the Evans Gambit, a sacrificial continuation.
3.d4, the Scotch Game, an immediate central strike.
3.Nc3 Nf6, the Four Knights Game, a more positional continuation.

Instead of 2...Nc6, Black may counterattack with 2...Nf6, the Petrov Defense. Also possible is 2...d6, the Philidor Defense, which is solid but not very popular because it allows White an easy space advantage, while Black may feel cramped.

White also has these alternatives to 2.Nf3:

2.f4, the King's Gambit, an aggressive pawn sacrifice which was featured in the Immortal Game.
2.Nc3, the Vienna Game, which has a variety of common plans.
2.Bc4, the Bishop's Opening, often transposing to the Italian Game or Vienna Game.
2.d4, the Center Game, which may continue 2...exd4 3.Qxd4 (3.c3 is the Danish Gambit).

Semi-open games: 1.e4, Black plays other than 1...e5

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Sicilian Defense

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Najdorf Variation

The most popular Black defense to 1.e4 at the top level is 1...c5,^[a] a Semi-Open Game known as the Sicilian Defense, known for leading to unbalanced positions. White's most common plan is 2.Nf3 and 3.d4 cxd4 4.Nxd4, known as the Open Sicilian, which often features sharp play. It was Bobby Fischer's favorite reply to 1.e4.

A very common line is 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3. From here, common variations include:

5...a6, the Najdorf Variation, which features a famous Poisoned Pawn Variation.
5...g6, the Dragon Variation, characterized by a kingside fianchetto.

Alternatively, after 2.Nf3, Black often plays 2...Nc6 or 2...e6 instead of 2...d6; the Sveshnikov Variation, perhaps Black's most ambitious try in the Open Sicilian, is a common line. Examples of notable variations outside of the Open Sicilian include:

2.Nf3 Nc6 3.Bb5, the Rossolimo Variation, which has a similar idea to the Ruy Lopez.
2.c3, the Alapin Variation, which aims to play d2-d4 supported by the possibility of cxd4.

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French Defense

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Caro–Kann Defense

Among other Semi-Open Games, the French Defense (1...e6, normally followed by 2.d4 d5) and the Caro–Kann Defense (1...c6, normally followed by 2.d4 d5) are also popular. They are solid openings where Black intends to play ...d5 only after preparing adequately. For both of them, White has the common four replies 3.Nc3, 3.Nd2, 3.e5, and 3.exd5.

The following four other moves are not uncommon:

1...d5, the Scandinavian Defense, is an immediate direct challenge to White in the center, but 2.exd5 Qxd5 3.Nc3 wins a tempo by forcing the queen to move again. 2...Nf6, a more modern line, is also seen.
1...d6 and 1...g6 can lead to the Pirc Defense and the Modern Defense, closely related hypermodern openings. 1...d6 can also transpose to the Philidor Defense.
1...Nf6, the least common of these, is the bizarre-looking^[25] Alekhine Defense, a hypermodern opening in which Black tempts White to win tempo with 2.e5 and establish an imposing pawn center, which would risk becoming overextended.

Closed games: 1.d4 d5

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Closed Game

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Queen's Gambit

The move 1.d4 offers similar benefits to development and central control as 1.e4, but unlike after 1.e4, where the e-pawn is undefended after the first move, the d-pawn is protected by White's queen. This slight difference has a tremendous effect on the opening. Also, compared with 1.e4 openings, transpositions are more common after 1.d4 than 1.e4.

The symmetrical moves 1.d4 d5 lead to what may be termed Closed Games. White's most popular reply to 1...d5 is 2.c4, the Queen's Gambit. Black can play 2...dxc4, the Queen's Gambit Accepted (QGA),^[b] but more often Black declines the pawn, via 2...e6, the Queen's Gambit Declined (QGD), or 2...c6, the Slav Defense. Both lead to an immense forest of variations, such as:

The Exchange Variation of the QGD, one of the most popular lines
The Semi-Slav Defense, which combines ...e6, ...c6, and ...Nf6, also very popular
The Tarrasch Defense, where Black plays ...e6 and ...c5, which has good piece mobility in mind

There are also some less common ways to decline the pawn, like 2...e5, the Albin Countergambit.

Instead of 2.c4, White could play an opening system, developing aiming for a particular formation without great concern over how Black chooses to defend. Systems are relatively easy to learn, but are rarely used at the top level because a well-prepared opponent playing Black can equalize fairly easily. Such opening systems played by White include the London System, Colle System, and Stonewall Attack.

Indian defenses: 1.d4 Nf6

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Indian Defense

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Nimzo-Indian Defense

The Indian systems are asymmetrical defenses to 1.d4 that employ hypermodern chess strategy and offer an unbalanced game. They avoid or delay occupying the center with pawns, instead aiming to control it from afar, such as with fianchettoed bishops.

Like against 1...d5, White's most common reply to 1...Nf6 is 2.c4. Black's most popular reply is 2...e6, freeing the king's bishop for development. It can lead to the Nimzo-Indian Defense,^[c] which meets 3.Nc3 with the pin 3...Bb4. White often plays 3.Nf3 to avoid it, or 3.g3, leading to the Catalan Opening. After 2...e6 3.Nf3, Black has several options:

3...Bb4+, the Bogo-Indian Defense, is not uncommon, but being able to play 4.Bd2 or 4.Nbd2 instead of 4.Nc3 (transposing to the Nimzo-Indian) seems to help White.
3...d5, transposing to the Queen's Gambit Declined.^[d]
3...b6, the Queen's Indian Defense, intending to fianchetto with Bb7, or to play Ba6.
3...c5, transposing to the Benoni Defense.

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Grünfeld Defense

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Budapest Gambit

2...g6, preparing a kingside fianchetto, is a more aggressive alternative for Black to 2...e6. It can lead to the risky King's Indian Defense (KID), which was Bobby Fischer's favorite defense to 1.d4. The Grünfeld Defense, which was played in the Game of the Century, is distinguished from the King's Indian by the move 3...d5, a less passive continuation.

Though 2...e6 and 2...g6 predominate, also of note are:

2...c5, the Benoni Defense, further explained below.
2...e5, the Budapest Gambit, a pawn sacrifice intending 3.dxe5 Ng4 (or 3...Ne4) that was popular in the early 20th century.
2...d6, the Old Indian Defense. It often transposes to the King's Indian Defense or another line.
2...Nc6, the Black Knights' Tango, where Black allows White to harass the knights by pushing pawns; White would win tempo, but could overextend.

Besides 2.c4, there are several other possible continuations for White, such as 2.Bg5, the Trompowsky Attack. Often, alternatives to 2.c4 will transpose to the Closed Games once Black plays d7-d5. Otherwise, the term Semi-Closed Game can be used to describe play after 1...Nf6 and the less common asymmetrical replies to 1.d4, examined below.

Other Black responses to 1.d4

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(Old) Benoni Defense

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Modern Benoni

1...c5, the Benoni Defense, is now more often reached by transposition from 1...Nf6.^[e] Instead of capturing or defending the d-pawn, the Benoni is best met by pushing by with the move d4-d5, claiming space. Play can^[f] develop into the Modern Benoni, an aggressive attempt by Black to gain active piece play at the cost of allowing White a pawn wedge at d5 and a central majority, popularized in the 1960s by Mikhail Tal. Alternatively, Black can play the Benko Gambit, sacrificing a pawn in order to apply pressure via opened lines on the queenside.^[g] Black's compensation is positional rather than tactical.

1...f5, the Dutch Defense, is an aggressive and unbalancing opening. Though more common in the past, it is still occasionally seen today. Beyond this, other possible replies are either rare or not particularly common while having little independent significance:

1...d6 might reach the Pirc Defense or Philidor Defense after 2.e4, more often reached via 1.e4 after 1...d6 2.d4. Alternatively, 2.c4 might lead to the King's Indian Defense, but Black could opt for 2...e5, the English Rat Defense. Another independent line is 2.Nf3 Bg4, the Wade Defense.
1...e6, the Franco-Indian Defense, allows White to transpose to the French Defense with 2.e4, but 2.c4 is more common, and will usually reach another 1.d4 opening.
1...g6, which usually reaches 1...Nf6 lines or 1...d6 lines.
1...c6, which offers transposition to the Caro–Kann Defense, or otherwise usually reaches the Slav Defense.
1...e5, the Englund Gambit, is an unsound pawn sacrifice not seen at the top level, though it sets some traps.

Flank openings

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English Opening

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	a	b	c	d	e	f	g	h

Symmetrical English

The flank openings are a group of White openings characterized by play on one or both flanks. Characteristic of a hypermodern playing style, they attack the center from the flanks, with pieces or pawns, rather than occupying it by playing d4 or e4. Though less common than 1.e4 and 1.d4 in popularity, 1.Nf3 and 1.c4 are still played with considerable frequency, especially at the top level.

1.c4, the English Opening, has several unique lines. Black's two replies with the most independent character are 1...c5, the Symmetrical English, and 1...e5, the Reversed Sicilian, but 1...Nf6, 1...e6, 1...g6, and 1...c6 are all common alternatives; by not controlling d4, they invite transposition into a 1.d4 opening, White may use the English in an attempt to avoid certain lines after 1.d4. For example, after 1.c4 Nf6 2.Nc3 e6, which might invite a Nimzo-Indian Defense after 3.d4 Bb4, White could instead play 3.e4, another line unique to the English.

1.Nf3, which has no standard name,^[h] results in the game transposing into either one of the openings that can emerge from 1.d4 (or from 1.c4; 1.Nf3 avoids the Reversed Sicilian line in the English by controlling e5), but there are unique openings such as the Réti Opening and King's Indian Attack (KIA). The Réti is characterized by White playing 1.Nf3, 2.c4 (or a later c4), fianchettoing one or both bishops, and not playing an early d4. The KIA is an example of an opening system that White may use in reply to most Black defenses. The characteristic setup is 1.Nf3, 2.g3, 3.Bg2, 4.0-0, 5.d3, 6.Nbd2, and 7.e4, although these moves may be played in several different orders. By adopting a set pattern of development, White can avoid a large amount of opening study.^[27]

Less common flank openings include:

1.g3, the King's Fianchetto Opening or Benko's Opening, is flexible and usually transposes into a known opening, such as the English Opening and the Catalan Opening.
1.b3, Larsen's Opening, also known as the Nimzo-Larsen Attack, intends a queenside fianchetto; it is occasionally seen in grandmaster play.
1.f4, Bird's Opening, where, like 1.d4 or 1.Nf3, White exerts control over the square e5. 1...d5 is a common reply, a reversed Dutch Defense; another possibility is 1...e5, a sharp pawn sacrifice known as From's Gambit.

Unusual first moves for White

1.e4, 1.d4, 1.Nf3 and 1.c4 are all very common opening moves. The fifth most common opening move, 1.g3, usually transposes into a standard line. Rarer choices occasionally seen in high level games include 1.b3 and 1.f4. The thirteen remaining possibilities are rarely played as they are not regarded as effective ways to exploit White's first-move advantage. They all share a single ECO code. The two most common of the thirteen moves are:

1.b4, sometimes called the Sokolsky Opening, is comparable to but rarer and riskier than 1.b3; the b-pawn is hanging.
1.Nc3, which is of a similar highly transpositional nature to 1.Nf3, but less flexible, as blocking the c-pawn with a knight matters more than the f-pawn.

Notes

1...c5 began to rival 1...e5 in the mid-20th century; 1...e5 remains common.
The QGA can also be reached by transposition if Black later plays ...dxc4. In the QGA, Black gives up the center for freer development and the chance to try to give White an isolated queen pawn with a subsequent ...c5 and ...cxd4.
The first of the Indian systems to gain full acceptance (1...d5 was dominant until the late 1940s), in the "Nimzo", advocated as early as 1913 by its namesake Aron Nimzowitsch, Black is prepared to trade a bishop for a knight to weaken White's queenside with doubled pawns.
Because White has played an early Nf3, White is unable to enter the main line of the Exchange QGD, which would have been possible had Black played 3...d5 instead of 3...Bb4 after 3.Nc3. Thus, the threat of the Nimzo-Indian (or "Nimzo") has significant consequences on the game. After 3.Nf3 d5 4.Nc3, there are many possible moves, including 4...c6, reaching the Semi-Slav Defense; 4...c5, the Semi-Tarrasch Defense; and 4...Bb4, the Ragozin Defense.
The most common is 1...Nf6 2.c4 c5; 3.d5 leads to the same position as 1.d4 c5 2.d5 Nf6 3.c4. 1...c5 can be called Old Benoni to distinguish from the 1...Nf6 move order. Also, instead of 2...c5, Black's ...c5 can be deferred until the third move or even later, which might occur if White avoids c2-c4. For example, after 1.d4 Nf6 2.c4 e6 3.Nf3 (avoiding the Nimzo-Indian Defense), 3...c5 4.d5 reaches a line of the Modern Benoni where White has committed to an early Nf3, ruling out an early f4, which occurs in the famous Taimanov Attack. It also gives Black the option to play 4...b5, the Blumenfeld Gambit.
e.g. after 1.d4 Nf6 2.c4 c5 3.d5 e6, or, transposing from the 1...c5 move order, 1.d4 c5 2.d5 Nf6 3.c4 e6 (or 2...e6 3.c4 Nf6).
If White accepts the pawn, after e.g. 4.cxb5 a6 5.bxa6, Black intends ...Bxa6 with the idea of ...Bxf1 if White later advances the e-pawn.
The Oxford Companion to Chess calls 1.Nf3 the Zukertort Opening, after Johannes Zukertort, but writes that he played 2.d4,^[26] which transposes into the Closed Games. Many sources call it the Réti Opening, but many other sources instead reserve that for, after 1.Nf3, the line 1...d5 2.c4.

Citations

"Phases of the game - Chess Strategy Online". www.chessstrategyonline.com. Retrieved 2021-03-30.
Hooper, David; Whyld, Kenneth (1992). The Oxford Companion to Chess (2 ed.). Oxford University Press. pp. 461–480. ISBN 0-19-280049-3.
"Book Move - Chess Terms". Chess.com. Retrieved 2021-03-30.
Garry Kasparov, Modern Chess part 1, p. 353
Fine 1952. sfn error: no target: CITEREFFine1952 (help)
Hansen, Lars Bo (October 7, 2008). How Chess Games are Won and Lost. Gambit. ISBN 978-1-906454-01-2.
Fine 1943. sfn error: no target: CITEREFFine1943 (help)
McHarg (AMcHarg), Andrew (31 January 2009). "The Importance of Development". Chess.com. Retrieved 2021-03-30.
Neustroev (Gertsog), Viktor (19 May 2020). "How to Control the Center (and Why It's Important)". Chess.com. Retrieved 2021-03-30.
Soltis, A. (2007). Transpo Tricks in Chess. Batsford. ISBN 978-0-7134-9051-0. See review at "Transpo Tricks in Chess – review". chessville.com. Archived from the original on 2008-04-18.
Jeremy Silman (1998). The Complete Book of Chess Strategy. Silman-James Press. p. 3. ISBN 1-890085-01-4.
Chassy, Philippe; Gobet, Ferdinand (2011). "Measuring Chess Experts' Single-Use Sequence Knowledge: An Archival Study of Departure from 'Theoretical' Openings". PLOS One. 6 (11) e26692. Bibcode:2011PLoSO...626692C. doi:10.1371/journal.pone.0026692. PMC 3217924. PMID 22110590.
Webb, Simon (1979). Chess for Tigers. Oxford University Press. ISBN 0-7134-8988-X.
Murray, H. J. R. (1913). A History of Chess. Oxford: Clarendon Press. pp. 782–83, 814–15. OCLC 643082.
Edward Winter, Chess Notes 3902, Openings nomenclature, 21 August 2005
Seirawan, Yasser; Silman, Jerry (2005), Winning Chess Tactics, Everyman Chess, p. 36, ISBN 1-85744-386-1
Hooper & Whyld, p281
Chess Opening Essentials 4, p. 11, ISBN 978-90-5691-308-3
This is in contrast to shogi opening theory, which generally categorizes openings by form regardless of the move sequences that brought about the form in what are sometimes called systems in western chess.
Whyld, Kenneth (1993). Learn Chess in a Weekend. Knopf/DK. p. 58. ISBN 978-0-679-42229-7.
Karpov, Anatoly (1988). The Open Game in Action. Batsford. ISBN 9780713460964.
Karpov, Anatoly (1988). The Semi-Open Game in Action. Batsford. ISBN 9780713460971.
Chess Opening Essentials 3, p. 38, ISBN 978-90-5691-308-3
Watson (2006), pp. 87–90
R.C. Griffith and M.E. Goldstein, Modern Chess Openings, Fourth Edition, 1925, p. 1.
Hooper & Whyld, p. 459
Larry Evans wrote of the King's Indian Attack, "White's resilient setup is truly magical. It throws both players on their own resources and eliminates the need of memorizing long-winded columns of analysis." Larry Evans, The Chess Opening for You, R.H.M. Press, 1975, p. 38. ISBN 0-89058-020-0.

References

Fine, Reuben (1990) [1943]. Ideas Behind the Chess Openings. Random House. ISBN 0-8129-1756-1.
Fine, Reuben (1983) [1952]. The World's Great Chess Games. Dover (orig. Andre Deutsch). ISBN 0486245128.
Kravtsiv, Martyn (2025). PCO: Practical Chess Openings. Gambit Publications. ISBN 9781805041047.