Dungeons & Dragons started as a war game by Tactical Studies Rules in 1973. In 1975, the company incorporated as TSR, Inc., and D&D took its place as the grandfather of all role-playing games. Although TSR, Inc. experimented with a number of other game genres, its first creation, D&D, remained the mainstay of TSR, Inc.'s corporate strength.

    In 1979, TSR, Inc. released the first book for Advanced Dungeons & Dragons, with more sophisticated divisions between races and classes and more complex rules for character development and game mechanics. AD&D swiftly surpassed the simpler D&D in popularity and is now the preeminent of the two games.

    In 1989, a second edition of AD&D was released that began shifting the game's focus to a point based system. Virtually all subsequent modules and reference books written for AD&D use second edition rules, and second edition AD&D is still the implicit core of D&D publishing. However, in 1995, TSR, Inc.
took the controversial step of publishing the first of a set of Player's Option rules books that continued to move D&D closer to a point based system. When the PO books were published, many players assumed they were the "third edition" of AD&D. However, TSR, Inc. vehemently denied this.