This version of Dungeons and Dragons was authored by Gary Gygax between 1977 and 1979 as a complete rewrite of the full set of the original Dungeons and Dragons rules, with an eye towards resolving inconsistencies and presenting a canonical form of the game. After the original edition of D&D was introduced in 1974, the game was split into two branches in 1977: the rules-light system of Dungeons & Dragons and the more complex, rules-heavy system of Advanced Dungeons & Dragons (AD&D). In 2000 the two branch split was ended when a new version was designated the 3rd edition, but dropped the "Advanced" prefix to be called simply Dungeons & Dragons.
Called Advanced Dungeons & Dragons, or AD&D, it is now commonly called "1st Edition".
Due to the Old School Renaissance (OSR) Movement and the rise of retroclones, sourcebooks and adventures that were not specifically put out by TSR are now grouped under AD&D First Edition (1e) Compatible Products