The Encyclopaedia of Chess Openings (ECO) is a book collection (now also a computer database) describing chess openings. The moves were taken from hundreds of thousands of games between masters, from published analysis in the Chess Informant since 1966, and then compiled by notable chess players. Both the ECO and the Chess Informant are published by the Serbian company Šahovski informator (homepage). These openings are typically provided in an ECO table that concisely presents the best opening lines.

Instead of the traditional names for the openings, ECO has developed a unique coding system that has also been used by other chess publications. There are five main categories, A-E, each of which is divided into a hundred sub-categories.

Main ECO codes

A

• White first moves other than 1.e4, 1.d4: Irregular openings
• 1.d4 without 1...d5, 1...Nf6: Atypical replies to 1.d4
• 1.d4 Nf6 without 2.c4: Atypical replies to 1...Nf6
• 1.d4 Nf6 2.c4 without 2...e6, 2...g6: Atypical Indian systems

B

• 1.e4 without 1...c5, 1...e6, 1...e5
• 1.e4 c5: Sicilian Defence

C

• 1.e4 e6: French Defence
• 1.e4 e5: Double King Pawn games

D

• 1.d4 d5: Double Queen Pawn games
• 1.d4 Nf6 2.c4 g6 + 3...d5: Grünfeld Defence

E

• 1.d4 Nf6 2.c4 e6: Indian systems with ...e6
• 1.d4 Nf6 2.c4 g6 without 3...d5: Indian systems with ...g6 (except Grünfeld)

See also

• List of chess openings for the full ECO codes

Chess openings

Encyclopaedia of Chess Openings | ECO-Codes | Enciclopedia de aperturas de ajedrez | Code ECO | Enciclopedia jugoslava delle aperture | Encyklopedia otwarć szachowych | ECO klasifikacija | ECO-klassificering