Where will I see an ECO code? How will I use it?Chess databases are powerful tools to improve your game. I'm building up to a post on that subject, first though we need to know about ECO codes. Because one of the easiest most powerful ways to search a chess database is using ECO codes. You'll see ECO codes displayed in most chess programs. Here are examples from Chess Openings Wizard and SCID vs PC. The SCID vs PC example being very typical of how you might see them displayed in any game database program.
What is an ECO?ECO Encyclopedia of Chess Openings a five volume set of books to classify all serious chess openings. Each volume is represented by a letter A, B, C, D, E, and 100 sub catagories 00 - 99. Publishing began in 1974. Here is a link to the full description in Wikipedia
A link to the publishers website http://www.chessinformant.org/eco-encyclopedia-of-chess-openings
An online index. https://web-beta.archive.org/web/20160913144956/http://www.chessinformant.org/content/eco/index.html
ECO codes with opening names and example games that can be downloaded. Free Internet Correspondence Games Server (FICGS) http://www.ficgs.com/directory_openings.html
ECO codes are useful when searching for games beginning with a particular set of moves, an opening.