ECO: A00 Irregular Openings
Irregular opening is a traditional term for any opening considered unusual or unorthodox. In the early 19th century it was used for any opening not beginning with 1. e4, e5 (the Open Game) or 1. d4, d5 (the Closed Game).
These openings are not popular with chess players, the standard opening references such as Modern Chess Openings (MCO) and Encyclopedia of Chess Openings (ECO) do not cover them in detail. Lewis comments that the irregular openings are "seldom played, because they are generally dull and uninteresting".
This index covers irregular or flank openings that don't begin with 1.d4 or 1.e4.
| No. | ECO | Notations | Name | Variations |
| 1. | A00 | 1. a3 | Anderssen's Opening | |
| 2. | A00 | 1. a3, a5, 2. b4 | Anderssens'Opening | Polish Gambit |
| 3. | A00 | 1. a3, e5, 2. h3 | Anderssen's Opening | Creepy Crawly Formation |
| 4. | A00 | 1. a3, g6 2. g4 | Anderssen's Opening | Anderssen's Spike |
| 5. | A00 | 1. a4 | Ware Opening | |
| 6. | A00 | 1. a4, e5 2. h4 | Crab Opening | |
| 7. | A00 | 1. b4 | Polish Opening | |
| 8. | A00 | 1. b4, c6 | Polish Opening | Outflank Variation |
| 9. | A00 | 1. b4, Nh6 | Polish Opening | Tuebingen Variation |
| 10. | A00 | 1. c3 | Saragossa Opening | |
| 11. | A00 | 1. d3 | Mieses Opening | |
| 12. | A00 | 1. d3, e5 | Mieses Opening | |
| 13. | A00 | 1. d3, e5 2. Nd2 | Valencia Opening | |
| 14. | A00 | 1. d3, e5 2. Nc3, Nc6 3. g3 | Venezolana Opening | |
| 15. | A00 | 1. e3 | Van't Kruijs Opening | |
| 16. | A00 | 1. e3, e5 2. c4, d6 3. Nc3, Nc6 4. b3, Nf6 | Amsterdam Attack | |
| 17. | A00 | 1. f3 | Gedult's Opening | |
| 18. | A00 | 1. f3, e5 2.Kf2 | Hammerschlag | |
| 19. | A00 | 1. g3 | Benko's Opening | |
| 20. | A00 | 1. g3, h5 | Lasker Simul Special | |
| 21. | A00 | 1. g3, e5 2. Nf3 | Benko's Opening | Reversed Alekhine |
| 22. | A00 | 1. g4 | Grob's Attack | |
| 23. | A00 | 1. g4, d5 2. Bg2, c6 3. g5 | Grob's Attack | Spike Attack |
| 24. | A00 | 1. g4, d5 2. Bg2, Bxg4 3. c4 | Grob's Attack | Fritz Gambit |
| 25. | A00 | 1. g4, d5 2. Bg2, Bxg4 3. c4, d4 | Grob's Attack | Romford Counter-Gambit |
| 26. | A00 | 1. h3 | Clemenz Opening | |
| 27. | A00 | 1. h3, e5 2. a3 | Global Opening | |
| 28. | A00 | 1. h4 | Anti-Borg Opening | |
| 29. | A00 | 1. Na3 | Durkin's Attack | Sodium Attack |
| 30. | A00 | 1. Na3, e5 2. Nc4, Nc6 3. e4 f5 | Durkin's Attack | Durkin Gambit |
| 31. | A00 | 1. Nc3 | Dunst Opening | |
| 32. | A00 | 1. Nc3, e5 | Dunst Opening | |
| 33. | A00 | 1. Nc3, e5 2. a3 | Battambang Opening | |
| 34. | A00 | 1. Nc3, c5 2. d4, cxd4 3. Qxd4, Nc6 4. Qh4 | Novosibirsk Opening | |
| 35. | A00 | 1. Nh3 | Amar Opening | |
| 36. | A00 | 1. Nh3, d5 2. g3, e5 3. f4, Bxh3 4.Bxh3, exf4 | Amar Opening | Gambit |
Unorthodox Openings
Source: Wikipedia
