The ECO codes were developed in the 1960's for the publication "Informant"
"A" codes are white first moves other than 1. e4 or 1. d4 (A00-A39), and 1. d4 without 1. ... d5, or 1. .. Nf6, and 1. d4 Nf6 without 2. c4, and 1. d4 Nf6 2. c4 without either 2. e6 or 2 g6, and 1. d4 f5.
"B" codes are 1. e4 without 1. ... c5, 1... e6 or 1. ... e5 (B00-B19) and 1. e4 c5 (B20-B99)
"C" codes are 1. e4 e6 and 1. e4 e5
"D" codes are 1. d4 d5 and 1. d4 Nf6 2. c4 g6 with 3. ... d5
"E" codes are 1. d4 Nf6 2. c4 e6 and 1. d4 Nf6 2. c4 g6 without 3. ... d5
Now, here's the trick to understanding why there won't ever be an "F" is that move order is irrelevant. If you get into a position where there is a white pawn on d4 and c4 and a black pawn on Nf6 and a black pawn on e6 then you're an "E" opening, even if the d4 pawn push happens on move 4 or 5. You've just got a wierd move order for the opening.
Question about ECO Code listing.
Got it! I guess the answer was simpler than I thought it would be. Can't say I wasn't hoping for a "we're not sure, well, we're still lookin' into that.." but thank you. Codes does not equal openings, there are several in each, which is something I just kind of connected. First post got it, not much of a topic I guess =) I appreciate it.
I did wonder about this topic when I first gazed upon my first opening's book, Modern Chess Openings and just like you, I never really bothered with it until now that I see Kingpatzer's description. lol
Most common openings are covered by multiple codes. For example, The French Defense is C01-C19
A list that connects names to codes that I find helpful: http://www.chessarch.com/library/0000_eco/index.shtml
Most common openings are covered by multiple codes. For example, The French Defense is C01-C19
Correction, French is C00 - C19
C00 is 1.e4 e6 w/o 2.d4
C01 is Exchange
C02 is Advance
C03 is Tarrasch w/o 3...c5, 3...Nf6, or 3...Nc6
C04 is Guimard (3.Nd2 Nc6)
C05 - C06 is Tarrasch w/ 3...Nf6
C07 is Tarrasch w/ 3...c5 and either NOT 4.exd5 OR 4.exd5 w/o 4...exd5
C08-C09 is Tarrasch with 3...c5 4.exd5 exd5
C10 is 3.Nc3 w/o 3...Nf6 or 3...Bb4
C11 is Steinitz (3...Nf6 4.e5). Note that 4.exd5 is back to C01.
C12 is MacCutcheon
C13 is 4.Bg5 w/o 4...Be7
C14 is 4.Bg5 Be7
C15 is Winawer w/o 4.e5
C16 is Winawer 4.e5 w/o 4...c5
C17-C19 is various Winawer lines after 4.e5 c5
C00 are lines that frequently transpose. When I am Black, if White plays anything other than 2.d4, they are likely to run into the Sicilian or some Queen's pawn opening, or a weird English.
1.e4 e6 2.f4 c5 is B21
Nonetheless, you are technically correct. ECO C00 is the French.
Start using search engines you'll be glad you did. If you aren't glad you did be sure to ask me for a refund. Here's what I found by typing "ECO Codes" into the GigaBlast SE, which I don't recommend using try IxQuick or DuckDuckGo if you have any privacy concerns, if not just use Google as long as you don't mind letting every advertiser in the universe know all about you.
Click on these links:
http://www.365chess.com/eco.php
http://www.ficsgames.org/eco.html
https://en.wikipedia.org/wiki/List_of_chess_openings
Warning Thread Disrail Ahead
Nimzo,
I frequently see you posting something along the lines of "Hey, learn how to use a search engine!" And while I certainly appreciate that knowing how to find information is a useful life skill, it seems to me that you completely miss the point of a disucssion forum, which is that social interactions are a heck of a lot more fun than google searchers.
Often, questions like the above lead to interesting discussions. And, frankly, if nothing else, it's a nice side-track from threads about "Is Fischer or Kasparov the Bestest Greatestest Most Awesomests Ever?!"
But really, Is Fischer of Kasparov the Bestest Greatestest Most Awesomests Ever?! I really want to know the answer to this Bestest Greatestest Most Awesomests Question Ever! 
Start using search engines you'll be glad you did. If you aren't glad you did be sure to ask me for a refund. Here's what I found by typing "ECO Codes" into the GigaBlast SE, which I don't recommend using try IxQuick or DuckDuckGo if you have any privacy concerns, if not just use Google as long as you don't mind letting every advertiser in the universe know all about you.
Click on these links:
http://www.365chess.com/eco.php
Google offers this kick-ash site: http://www.sahovski.co.rs/eco/
Warning Thread Disrail Ahead
Nimzo,
I frequently see you posting something along the lines of "Hey, learn how to use a search engine!" And while I certainly appreciate that knowing how to find information is a useful life skill, it seems to me that you completely miss the point of a disucssion forum, which is that social interactions are a heck of a lot more fun than google searchers.
Often, questions like the above lead to interesting discussions. And, frankly, if nothing else, it's a nice side-track from threads about "Is Fischer or Kasparov the Bestest Greatestest Most Awesomests Ever?!"
+1. Chess forums are for discussing chess stuff.
Often, questions like the above lead to interesting discussions. And, frankly, if nothing else, it's a nice side-track from threads about "Is Fischer or Kasparov the Bestest Greatestest Most Awesomests Ever?!" Kingpatzer
I'm not in favor of using SEs 100% of the time and never asking anyone for help, I've needed help from folks from time to time myself when SEs didn't work for me (or I was looking for opinions).
BUT I don't see the pt of asking for help for simple questions an SE can answer or the strange attitude that some people don't need to ever use them, they can just let others look stuff up for them all the time.
It's called "community." It's the point of online forums. Human interactions are more interesting than non-human interactions most of the time for most people.
It's called "community." It's the point of online forums. Human interactions are more interesting than non-human interactions most of the time for most people.
+1 again
Is Fischer or Kasparov the Bestest Greatest Most Awesomests Ever?! I still haven't been answered!?
Shepi13 - maybe.
Back to the topic:
Outside of teh ECO codes, there's also the NIC codes for chess opening classification. But I don't think they're used anywhere outside of NICBase and NIC Yearbooks.
I can't find anything online that really outlines how they work either. As far as I can tell they're based more or less on the common opening names.
+2 +2
@Nimzo - I said to post links in case no one wanted to answer, I guess I wasn't sure if it was a stupid question. When I googled it I got lists of ECO code openings - and still wondered why it stopped at 500. I do alot of research over the net, and have no problems with SE's, try googling: Why does ECO Codes stop at 500 - maybe not for you, but I get absolutely nothing with useful information.
@Shepi- No, Alekhine is the most greatest, awesomest ever!
When I started playing a little over a year ago, I noticed the ECO codes next to the openings I would study. I never gave it much thought, since I figured there were millions, or at least thousands. As it turns out, there are 500. At least that's what I think, and that's part of my question. Does letters A-E and numbers 00-99 cover every possible opening? Is the number exactly 500? Are we sure there will never be a F00-F25 at least? Do they get added one by one or are they introduced and recognized in groups? If the first question wasn't loaded, I loaded it for you
I basically want to know if there is/will ever be/could possibly be more openings added to the ECO list in the future, in a nutshell, and I appreciate any information. If you don't feel like explaining, post links, I just can't seem to find much on this particualar question. Thanks.