ChessOps - ECO CODING SYSTEM - SHORTLIST

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ECO coding is a unique system of classifying all chess openings by means of 500 codes (from A00 to E99). It first appeared in 1966 in the initial publication of Chess Informant (a regular analysis periodical now approaching its 100th issue), and was then used as the classification basis in an Encyclopedia of Chess Openings, a virtually languageless reference work first published in 1974-9 by Chess Informant in 5 volumes (A to E, each covering one classification group). This led to it becoming known as the ECO system, now a FIDE-accepted standard classification used worldwide.

Revised volumes of the Encyclopedia of Chess Openings are published from time to time, providing a comprehensive resource collection of modern opening theory. Its 3,000 pages give examples from over 150,000 games and contain analyses contributed by top chess players from all over the world.

At its most basic level, ECO uses five code groups to cover all start-moves, described algebraically as:

Each code group has "divisions and sub-divisions of 10" whereby for example group A has categories A0-A9, and category A0 expands into codes A00 to A09. Thus group D ("1.d4 with early ..d5") includes a category D2 (classified as "1.d4 d5, 2.c4 dxc4", the Queen's Gambit Accepted), which in turn includes ECO code D22 ("1.d4 d5, 2.c4 dxc4, 3.Nf3 a6, 4.e3", the Alekhine Variation and off-shoots). All opening moves are thus categorised under one of the 500 ECO codes, with the more popular openings and defences found under certain "ranges" of codes:

Below is a summary shortlist of the main ECO codes, with links to some of the equivalent openings (NB: information is from various sources in Dec.2007 and has not been fully checked yet for 100% accuracy, being work still in progress Dec. 2009!):