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). The standard game was eventually expanded into a series of five box sets by the mid-1980s before being compiled and slightly revised in 1991 as the Dungeons & Dragons Rules Cyclopedia. Meanwhile, the 2nd edition of AD&D was published in 1989. In 2000, the 3rd edition, called simply Dungeons & Dragons, debuted. The 4th edition was published in 2008. The 5th edition was released in 2014.