The Encyclopaedia of Chess Openings (ECO) is a reference work describing the state of opening theory in chess, originally published in five volumes from 1974 to 1979 by the Serbian company Šahovski Informator (). It is currently undergoing its fifth edition.

The moves are taken from thousands of master games and from published analysis in Informant and compiled by the editors, most of whom are grandmasters, who select the lines that they consider most relevant or critical. The chief editor since the first edition has been Aleksandar Matanović (1930–2023). The openings are provided in an ECO table that concisely presents the opening lines considered most critical by the editors. ECO covers the openings in more detail than rival single-volume publications such as Modern Chess Openings and Nunn's Chess Openings, but in less detail than specialized opening books.

The books are intended for an international audience and contain only a small amount of text, which is in several languages. The bulk of the content consists of diagrams of positions and of annotated chess moves presented in Figurine Algebraic Notation.

Instead of the traditional names for the openings, ECO has developed a coding system that has also been adopted by other chess publications and chess websites. There are five main categories, "A" to "E", corresponding to the five volumes of the earlier editions, each of which is further subdivided into 100 subcategories, for a total of 500 codes. The term ECO is often used as a shorthand for this coding system. ECO code is a registered trademark of Chess Informant.

Openings covered

Volume A: Flank openings English Opening Benoni Defence Dutch Defence Réti Opening Benko Gambit Old Indian Defence Bird's Opening Anti-Indian systems (Trompowsky Attack, Torre Attack, Richter–Veresov Attack) Irregular openings, etc.

Volume B: Semi-Open Games other than French Defence Sicilian Defence Caro-Kann Defence Pirc Defence Alekhine's Defence Modern Defence Scandinavian Defence, etc.

Volume C: Open Games and French Defence Ruy Lopez French Defence Petrov's Defence Vienna Game Centre Game King's Gambit Philidor Defence Italian (Giuoco Piano, Evans Gambit, Hungarian Defence, and Two Knights) Scotch Game Four Knights Game, etc. King's Pawn Opening, etc. (covers unusual/rare 1. e4 openings such as the Elephant Gambit and Ponziani Opening).

Volume D: Closed Games and Semi-Closed Games (including Grünfeld Defence but not other Indian Defences) Queen's Gambit Accepted Declined (Slav, Orthodox, Tarrasch, Tartakower, Albin Countergambit, etc.) Grünfeld Defence Queen's Pawn Game, etc.

Volume E: Indian Defences (other than Grünfeld Defence and Old Indian Defence) Nimzo-Indian Defence Queen's Indian Defence King's Indian Defence Catalan Opening Bogo-Indian Defence, etc.

First edition The first edition was published in the following years: Volume A: 1979 Volume B: 1975 Volume C: 1974 Volume D: 1976 Volume E: 1978 +1st Edition ContributionsAuthorCodesABCDE70–79, 98–9927–29, 47–4900–0525–2900–01, 94–9532–3760–6567–6986–89, 92–9513–1470–79, 98–9927–29, 47–4956–5782–8397–9943–4440–4202–0506–07, 93–940628–2931–3290–9210–1510, 12, 15, 17, 36–3950–5546, 56–5960–6587–8968, 77–7920–26, 70–79, 80–81, 97–9845–4630–3492, 9938–39, 80, 90–9110–11, 20–2353–55, 65–6645, 48–4902–0358–5995–9680–81, 84–8554–5562–6485–8983–8473–7604–0530–31, 34–3543–44, 47–4967, 96–9915–1943, 50–5140–422506–07, 93–9400–01 00–01, 1633–3485–8667–6987–8916–1962–6930, 35–3608–09, 15–192582–8397–9950–52, 5606–09, 37–3870–72, 76–7900–050203, 46–4707–0940–4224–26, 5369–70, 90–9120–2444, 50–53, 60–61, 86, 90–91, 93–9626–2914, 73–7562–6480–82, 83–8404-0545–4696–9780–81, 84–8502–0507, 0927, 54–56, 58–59, 8710–1412–1382–8534–3940–43, 45–4920–2430–31, 40–4506, 11, 18–1957–5916–1962–6930, 35–3608–09, 15–1908, 60–61, 7132–3381–84, 92–9360–6338–3957, 88–897264–660066–6952 Second edition The second edition was published in the following years: Volume A: 1996 Volume B: 1984 Volume C: 1981 Volume D: 1987 Volume E: 1991

+ Volume B (1984) Author Codes 13–14 04–05, 18–19 13–14 28–29 10, 12, 15, 17, 36–39 70–79 95–99 20–21, 23–26 02–03 80–85 30–31, 34–35 28–29, 87 00–01, 16 60–69 06, 11 57, 88–89 07–09 44, 50–53, 86, 90–94, 96 27, 54–56, 58–59 22, 33 40–43, 45–49 60–69 32

Third edition The third edition was published in the following years: Volume A: 1999 Volume B: 1997 Volume C: 1997 Volume D: 1998 Volume E: 1998

Fourth edition The fourth edition was published in the following years: Volume A: 2001 Volume B: 2002 Volume C: 2000 Volume D: 2004 Volume E: 2008

Fifth edition The fifth edition was published in the following years: Volume C: 2006 Volume B part 1 [ECO codes: B00–B49]: 2020 Volume B part 2 [ECO codes: B50-B99]: 2021

See also Chess annotation symbols – ECO uses symbols instead of text Chess Informant List of chess books Modern Chess Openings Opening book

References

Bibliography

External links Publisher's site ECO codes with names