[Erax]

This is the timeline as I know it : First there were the small booklets, called D&D and first released in 1976 or 77, with new booklets being released over the years (Castle Greyhawk, Blackmoor and so on). Then 'AD&D' (three hardback, large-sized volumes) was released sometime between 1979 and 1981. At the same time, D&D was completely rewritten to become a simplified Version of the game, with less options and cleaner rules.

For a long time, D&D and AD&D existed simultaneously; D&D went through several Versions, known as the 'blue box', 'red book', 'white book' and so on. AD&D kept expanding and eventually became 11 different hardback volumes, of which I own 6. The awkward parts of the rules were never rewritten, they were just added to.

Sometime around 1988, 2nd edition AD&D came out. It fixed many things but did not change the basics of the race, class and level system.

Then in more recent years, the old D&D was extinguished and 3rd edition AD&D was released, only it had been renamed D&D. I can't say much about it because I still play (which is almost never) under a mishmash of 1st and 2nd edition rules. However, I do play Star Wars D20, and if that is in any way similar to 3rd Edition, it means they have finally fixed the most irritating aspects of the original game.