Classic Dungeons & Dragons is used in gaming circles to describe a family of rules sets. Though it does not have a fixed definition, it is usually taken to main the Moldvay B/X sets, the BECMI series of boxed sets, and the Rules Cyclopedia. These rules post-date Original Dungeons & Dragons, and diverge from Advanced Dungeons & Dragons.

A rule of thumb might be, versions of Dungeons & Dragons which you can use with certain classic modules, for instance B4: The Lost City, without modification.

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