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A chess opening theory table or ECO table (Encyclopaedia of Chess Openings) presents lines of moves, typically (but not always) from the starting position. Notated chess moves are presented in the table from left to right. Variations on a given line are given horizontally below the parent line.

## Arrangement

Chess opening theory tables are commonly published in opening books with annotations by experienced chess players. These tables are typically arranged in a compact manner to allow experienced players to see variations from a position quickly. Usually, the table indicates that either White or Black has equal, slightly better, or better chances at the end of the variation. Often, this information is distilled down to mere symbols ("Σ" for example) or the percentage of games (usually tournament games) where White won – no information is usually given on what the assessment is based on or how to proceed in the game.

## Shortcomings

Chess opening theory books that provide these tables are usually quite large and difficult for beginners to use. Because the table entries typically do not include the themes or goals involved in a given line, beginners will either try to memorize the tables or simply drown in the detail. The Wikibook Chess Opening Theory aims to bridge this gap by providing this type of information at the end of each line.

## Notation

Typically, each table has a heading indicating the moves required to reach the position for which the table provides an analysis. The example below is for the opening position, so no moves are shown in the heading. The first row provides the move numbers with subsequent rows representing different variations. Since the initial position is not always the opening position, these numbers will not always start at "1." White half-moves are shown above black half-moves. Ellipses (...) represent moves that, for the variation, are identical to the variation above. Bold type indicates that another variation is considered elsewhere – usually in another table. A hyphen (-) or en dash (–) indicates that the variation transposes to a variation elsewhere. Transpositions are common in chess – a given position can often be reached by different move orders – even move orders with more or fewer moves. The table may also provide percentage of games won by white for each variation, based on the results of the games considered in creating the table.

## Development

Chess openings are studied in great depth by serious players. "Novelties", or new, previously unexplored variations are often discovered and played by professional players. These new lines can refute lines that were previously thought to be sound. The games that represent this discovery process are represented in these ever-changing and expanding tables. With the advent of computer databases, even the most casual player can explore an opening line deeply, looking for novelties to spring on their opponents.

## Example

1 2 3 4 5 6 7 8 Σ%
1 Nf3
c5
c4
Nf6
Nc3
d5
cxd5
Nxd5
d4
Nxc3
bxc3
g6
e4
Bg7
Rb1
0-0
25: 42%
2 ...
d5
d4
Nf6
c4
c6
Nc3
e6
e3
Nbd7
Qc2
Bd6
b3
0-0
Be2
b6
16: 56%
3 ...
Nf6
c4
e6
Nc3
Bb4
Qc2
0-0
a3
Bxc3
Qxc3
b6
b4
a5
Bb2
axb4
28: 63%
4 d4
d5
c4
dxc4
Nf3
e6
e3
Nf6
Bxc4
c5
0-0
a6
Bb3
cxd4
exd4
Nc6
33: 50%
5 ...
...
...
c6
Nf3
Nf6
Nc3
dxc4
a4
Bf5
Ne5
Nbd7
Nxc4
Qc7
g3
e5
28: 63%
6 ...
Nf6
c4
g6
Nc3
Bg7
e4
d6
Nf3
0-0
Be2
e5
Be3
c6
d5
Ng4
28: 57%
7 ...
...
...
...
...
d5
cxd5
Nxd5
e4
Nxc3
bxc3
Bg7
Nf3
c5
Be3
Qa5
16: 59%
8 ...
...
...
e6
Nf3
d5
Nc3
Be7
Bf4
0-0
e3
c5
dxc5
Bxc5
a3
Nc6
28: 52%
9 ...
...
...
...
Nc3
Bb4
Qc2
0-0
a3
Bxc3†
Qxc3
b6
Bg5
Bb7
f3
h6
23: 67%
10 ...
...
...
...
...
...
...
d5
cxd5
Qxd5
e3
c5
Bd2
Bxc3
Bxc3
cxd4
13: 46%
11 e4
e6
d4
d5
Nc3
Nf6
e5
Nfd7
f4
c5
Nf3
Nc6
Be3
cxd4
Nxd4
Bc5
31: 77%
12 ...
e5
Nf3
Nf6
Nxe5
d6
Nf3
Nxe4
d4
d5
Bd3
Nc6
0-0
Be7
c4
Nf6
16: 63%
13 ...
...
...
...
...
...
...
...
...
...
...
...
...
...
...
Nb4
20: 50%
14 ...
...
...
Nc6
Bb5
Nf6
0-0
Nxe4
d4
Nd6
Bxc6
dxc6
dxe5
Nf5
Qxd8+
Kxd8
24: 60%
15 ...
...
...
...
...
a6
Ba4
Nf6
0-0
Be7
Re1
b5
Bb3
d6
c3
0-0
35: 63%
16 ...
c5
Nf3
Nc6
Bb5
g6
0-0
Bg7
Re1
e5
Bxc6
dxc6
d3
Ne7
Be3
b6
29: 50%
17 ...
...
...
...
Nc3
e5
Bc4
d6
d3
Be7
0-0
Nf6
Nh4
Nd4
g3
Bg4
16: 59%
18 ...
...
...
...
d4
cxd4
Nxd4
Nf6
Nc3
e5
Ndb5
d6
Bg5
a6
Na3
b5
31: 56%
19 ...
...
...
d6
d4
cxd4
Nxd4
Nf6
Nc3
a6
Be2
e6
f4
Be7
Be3
0-0
28: 45%
20 ...
...
...
...
...
...
...
...
...
...
Be3
e6
f3
b5
g4
h6
32: 52%

## External sources of chess opening theory tables

• John Nunn (editor), Graham Burgess, John Emms, Joe Gallagher (1999), Nunn's Chess Openings. ISBN 1-85744-221-0.
• Nick de Firmian, Walter Korn (1999), Modern Chess Openings: MCO-14. ISBN 0-8129-3084-3.
• Aleksandar Matanović (editor), Encyclopaedia of Chess Openings, 5 volumes (Belgrade: Šahovski informator)