Encyclopaedia of Chess Openings (ECO) Overview
Encyclopaedia of Chess Openings
Definition
The Encyclopaedia of Chess Openings (ECO) is a comprehensive, standardized reference system for classifying chess openings. Published by Chess Informant (Šahovski informator) beginning in the 1970s in Belgrade, it organizes the vast body of opening theory into five letter-coded volumes (A–E), each subdivided into numerical codes from 00 to 99 (e.g., B90). ECO entries present opening lines and variations using concise Informant symbols and minimal prose, making the work language-independent and globally usable.
How it is used in chess
- Opening identification: Players, authors, and commentators refer to openings by their ECO codes (e.g., “B90” for the Najdorf Sicilian) to quickly pinpoint the exact system or subline.
- Databases and PGN: Chess databases tag games with an ECO field (e.g., [ECO "C65"]) to enable searching, filtering, and statistical analysis by opening family.
- Preparation and study: Coaches and players use ECO codes to organize repertoires, track transpositions, and build targeted study files (e.g., “E97 King’s Indian: Mar del Plata”).
- Publishing and annotation: Books, magazines, and online portals standardize opening references using ECO so readers can navigate diverse sources consistently.
Classification at a glance
ECO codes consist of a letter A–E (broad family) plus two digits (00–99) indicating specific branches. While exact ranges are technical, a practical overview is:
- A-codes: Flank and irregular systems (e.g., English, Réti, Dutch, Benko/Benko Accepted, various 1.d4 sidelines, and uncommon first moves).
- B-codes: Semi-open games excluding the French (e.g., Scandinavian, Alekhine, Pirc/Modern, Caro-Kann, and the Sicilian Defence including Najdorf and Sveshnikov lines).
- C-codes: Open games and the French Defence (e.g., 1.e4 e5—Ruy Lopez, Italian, Scotch—and French C00–C19).
- D-codes: Closed and semi-closed Queen’s Pawn systems (e.g., Queen’s Gambit Accepted/Declined, Slav/Semi-Slav, Tarrasch; Grünfeld coverage sits in the high D-codes).
- E-codes: Indian Defences and related systems (e.g., Catalan and Queen’s/ Nimzo-Indian families, and the King’s Indian Defence main lines).
Examples with codes and first moves
- B90 — Sicilian Defence, Najdorf: 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6
- C65 — Ruy Lopez, Berlin Defence: 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6
- D43 — Semi-Slav Defence: 1. d4 d5 2. c4 e6 3. Nc3 c6
- B01 — Scandinavian Defence: 1. e4 d5
- B12 — Caro-Kann, Advance Variation: 1. e4 c6 2. d4 d5 3. e5
- A57 — Benko (Volga) Gambit: 1. d4 Nf6 2. c4 c5 3. d5 b5
- E97 — King’s Indian Defence, Orthodox Main Line: 1. d4 Nf6 2. c4 g6 3. Nc3 Bg7 4. e4 d6 5. Nf3 O-O 6. Be2 e5 7. O-O Nc6 8. d5 Ne7
Strategic and historical significance
ECO unified opening terminology across languages and eras, enabling a common “index” for theory. Its language-independent symbols (like +=, ∞, etc. in the Informant style) helped grandmasters share evaluations concisely. The five-volume structure became the backbone for modern databases and for how players discuss openings—“This game reached B90” instantly conveys a wealth of context. ECO’s influence surged alongside professional preparation and the database era: codes became essential metadata for sorting, preparing novelties, and studying transpositions.
Historically, ECO was edited by leading masters under the Chess Informant umbrella and updated across editions as theory advanced. The system also inspired complementary works (e.g., Nunn’s Chess Openings, Modern Chess Openings) and remains deeply integrated into today’s software and opening explorers.
Practical usage tips
- PGN metadata: Most software recognizes the ECO tag (e.g., [ECO "B90"]) and will auto-detect the code from the moves.
- Repertoire organization: Group your files by ECO ranges (e.g., “B90–B99 Najdorf”) to streamline study and avoid overlap.
- Transpositions: The same ECO can be reached via different move orders; learn typical pawn structures and piece placements, not just move sequences.
- Updates: Codes are stable, but novelties shift the “main lines.” Use ECO to orient yourself, then verify the latest theory with a current database.
Notable examples and context
- Berlin Revival (C65–C67): Vladimir Kramnik’s adoption in the World Championship (Kramnik vs. Kasparov, 2000) popularized the Berlin and reshaped 1.e4 e5 theory.
- Najdorf Era (B90–B99): A mainstay of dynamic Sicilian play for decades, central in the repertoires of Fischer, Kasparov, and many modern tacticians.
- King’s Indian Battles (E60–E99): Fierce strategic fights, famously embraced by players like Bronstein, Fischer, and Kasparov; the Mar del Plata structures remain a theoretical battleground.
- Benko/Volga Gambit (A57–A59): A model of long-term positional compensation for a pawn; understanding typical queenside pressure is more important than memorizing every branch.
Interesting facts and anecdotes
- Language-independent design: ECO’s Informant symbols and concise variations were conceived so a single edition could serve the entire world chess community.
- Sticky shorthand: Many players casually say things like “I play B12 vs. 1.e4,” meaning a Caro-Kann Advance-based repertoire, or “He’s a B90 specialist.”
- Opening explorers: Most major online platforms display ECO alongside the opening name to help users situate their games in the broader theoretical map.
- From paper to pixels: Originally five printed volumes (A–E), ECO’s taxonomy now underpins digital databases, where it’s combined with engine evaluations and game statistics.