ECO: Encyclopaedia of Chess Openings
ECO (Encyclopaedia of Chess Openings)
Definition
“ECO” stands for Encyclopaedia of Chess Openings, a five-volume reference work first published in the 1970s by the Serbian publishing house Sahovski Informator. Each volume catalogues chess openings through an alphanumeric code—ranging from A00 to E99—that is now universally used by players, authors, coaches, databases, and chess engines to identify specific opening systems and sub-variations with concise precision.
Origin and Structure
The creators, Grandmasters Aleksandar Matanović and Milivoje Molerović, sought a language-neutral way to classify the ever-expanding body of opening theory. They divided all openings into five broad “volumes,” each assigned a letter:
- A00–A99: Flank openings and uncommon 1.d4 or 1.e4 sidelines (e.g., Réti Opening).
- B00–B99: Semi-open games starring 1.e4 other than the French or Caro-Kann (e.g., Sicilian Defence).
- C00–C99: 1.e4 e6 French, 1.e4 e5 Open Games, and the Petrov.
- D00–D99: Closed 1.d4 openings, notably the Queen’s Gambit and Grünfeld.
- E00–E99: Indian Defences (Nimzo-Indian, King’s Indian, Catalan, etc.).
Within each volume, the numbers 00-99 drill down to finer branches. For example, E97 refers specifically to the King’s Indian Defence, Classical System, Makogonov variation after 9.Bf4.
How It Is Used in Chess
ECO codes function as the “Dewey Decimal System” of openings:
- Study & Preparation – Players label repertoire files and search databases by ECO code (e.g., “I need fresh ideas in B33 Najdorf”).
- Publishing & Commentary – Books, magazines, and digital platforms print codes beside game scores so readers instantly know the opening context.
- Engine & GUI Integration – Chess engines auto-tag positions; graphical interfaces often display the ECO code once the opening is recognized.
- Tournament Bulletins – Organizers categorise thousands of games efficiently (“Round 5 had five games in D37 Queen’s Gambit Exchange”).
Strategic and Historical Significance
Before ECO, the same opening line was frequently known by multiple names in different countries, causing confusion. The standardized code:
- Streamlined international communication among players and authors;
- Encouraged systematic expansion—new discoveries are appended inside the existing code rather than inventing a new “defence” name;
- Became the backbone of modern opening theory databases such as ChessBase and MegaDatabase;
- Served as an objective shorthand that avoids sponsor or national bias.
Examples
Below are three illustrative ECO snippets. Moves are given in algebraic notation; the ECO code appears in brackets.
- A45 – 1.d4 Nf6 2.Nf3: a flexible Queen’s Pawn opening leading to setups such as the Colle or Torre.
- B33 – Sicilian Defence, Sveshnikov: 1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 e5.
- E97 – King’s Indian, Classical, Makogonov:
Notice how the ninth move 9.Bf4 distinguishes E97 from E94–E96 branches.
Interesting Facts and Anecdotes
- While early editions were printed in figurine algebraic language-neutral notation, later editions added small diagrams every few moves—dubbed “ECO diagrams” by generations of students.
- Two codes—C42 (Petrov) and B12 (Caro-Kann)—became humorous shorthand in Soviet training camps: “If you play C42 against him, expect a draw before lunch.”
- During the 1997 IBM match, commentators flashed “D45” on screen to show that Kasparov vs. Deep Blue had entered a Semi-Slav Meran—a first in a world championship involving a computer.
- The codes are occasionally re-evaluated. When the Berlin Wall (1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6) surged after Kramnik-Kasparov 2000, the editors expanded C67–C69 to allocate more sub-lines for the endgame-heavy Berlin.
In Summary
ECO is more than a set of codes; it is the global standard that underpins every serious discussion of opening theory. Whether skimming a grandmaster monograph or scrolling through an online database, recognizing “B90” or “D37” instantly places you in the right strategic neighborhood—one of the many quiet ways ECO has shaped the modern chess landscape.