Bottle of Smoke wrote:
In the beginning, there was Chainmail!. It was a system for simulating medieval combat, and nothing more. It was not a role-playing game. And they saw that it was good.
Then came Dungeons & Dragons. You remember this as the “boxed set” you got for your birthday. It consisted of the Basic Set (which covered characters through 3rd level), the Expert Rules, and the World of Greyhawk. And they saw that it was good.
Then Gygax’s bunch decided to make an Advanced version of the rules. They called it Advanced Dungeons & Dragons. It consisted of the Monster Manual, the Player’s Handbook, and the Dungeon Masters’ Guide (published in that order). Nowadays, we refer to this as “AD&D 1st Edition”, but at the time they didn’t know there were going to be multiple editions of AD&D. The problem with this new AD&D system, though, was it was just different enough from the original D&D rules to be incompatible with them. Many die-hard enthusiasts of Original D&D refused to accept it. Thus, D&D and AD&D began to evole independently of one another.
Several years later, Gygax and company published the first major AD&D revision, in a book called Unearthed Arcana. It incorporated new character classes inspired by the D&D Saturday morning cartoon. (I am not kidding about that.) The paladin character class was vastly changed. Bunches of new magic items and spells were added. Unearthed Arcana is still considered part of the 1st Edition oevre, though.
The next major revision of the AD&D rules was the publication of Advanced Dungeons & Dragons, 2nd Edition in 1989. Its most striking feature was that Gary Gygax had nothing whatsoever to do with it. There was much rejoicing. Unfortunately, it also eliminated the Monk character class. (I used to think they also eliminated psionics from 2nd Edition, but as it turns out, Steve Winter wrote an optional module called The Complete Guide to Psionics as a 2nd Edition supplement.)
Now, just this year, Wizards of the Coast has published D&D 3rd Edition. Despite its name, it is a revision of the AD&D rules, not the original D&D rules. The dropping of the “A” was little more than a formality – despite its die-hard adherents, non-Advanced D&D was all but dead, and Wizards of the Coast opted not to support it at all. With 3rd Edition there is no more AD&D/D&D schism, it’s all called D&D. And they’re planning to release their psionics rules in March.
So, in order, the editions were:[ul][li]Original D&D[/li][li]AD&D (1st Edition)[/li][li]Unearthed Arcana[/li][li]AD&D 2nd Edition[/li]D&D 3rd Edition[/ul]