Editing Encyclopaedia of Chess Openings (section)

== Main ''ECO'' codes ==
{{main|List of chess openings}}

===A===
* White first moves other than 1.e4, 1.d4 (A00–A39)
* 1.d4 without 1...d5, 1...Nf6 or 1...f5: Atypical replies to 1.d4 (A40–A44)
* 1.d4 Nf6 without 2.c4: Atypical replies to 1...Nf6 (A45–A49)
* 1.d4 Nf6 2.c4 without 2...e6, 2...g6: Atypical [[Indian Defence|Indian systems]] (A50–A79)
* 1.d4 f5: [[Dutch Defence]] (A80–A99)

===B===
* 1.e4 without 1...c6, 1...c5, 1...e6, 1...e5 (B00–B09)
* 1.e4 c6: [[Caro–Kann Defence]] (B10–B19)
* 1.e4 c5: [[Sicilian Defence]] (B20–B99)

===C===
* 1.e4 e6: [[French Defence]] (C00–C19)
* 1.e4 e5: [[Open Game|Double King Pawn games]] (C20–C99)

===D===
* 1.d4 d5: [[Closed Game|Double Queen Pawn]] games (D00–D69)
* 1.d4 Nf6 2.c4 g6 with 3...d5: [[Grünfeld Defence]] (D70–D99)

===E===
* 1.d4 Nf6 2.c4 e6: [[Indian Defence|Indian systems]] with ...e6 (E00–E59)
* 1.d4 Nf6 2.c4 g6 without 3...d5: Indian systems with ...g6 (except Grünfeld) (E60–E99)