Blackmoor is a fantasy role-playing game campaign setting generally associated with the game Dungeons & Dragons. It originally evolved in the early 1970s as the personal setting of Dave Arneson, the co-creator of Dungeons & Dragons, first as a setting for Arneson's miniature wargames, then as an early testing ground for what would become D&D. Blackmoor is the longest continuously played fantasy role-playing campaign in existence.
The original Blackmoor product was published by Tactical Studies Rules (TSR) in 1975, as the second supplement to D&D (the first being Greyhawk). The booklet was named for the original role-playing campaign world by Dave Arneson, who also wrote this booklet. It added rules, monsters, treasure, and the first published role-playing game adventure, "Temple of the Frog". Despite the name, however, it did not include any information on the setting itself.
For various reasons, TSR published two different versions of their flagship game line. Over the course of several supplements, the Basic Dungeons & Dragons developed its own campaign setting, referred to at first simply as the Known World and later as Mystara. When the history of Mystara was codified, it was established that Arneson's Blackmoor had existed in the world's distant past, achieved a technologically advanced civilization and then destroyed itself in a global catastrophe which shifted the planet's axis.
Though its influence was now central to at least one of TSR's published worlds, the actual setting of Blackmoor as Arneson described it had yet to be presented. This was finally remedied in the mid-1980s through the DA series of expansion modules, which carried a party of adventurers into Mystara's past to visit Blackmoor. The first of these, DA1 "Adventures in Blackmoor", described in general the geography and politics of Blackmoor and the means by which the characters travel there. DA2 "Temple of the Frog" expanded the scenario that had appeared in the original Blackmoor supplement. DA3 "City of the Gods" explored the starship crashed near the Kingdom of Blackmoor, from which the setting's intentional anachronisms derived. DA4 "The Duchy of Ten" dealt with a horde of invading barbarians, but was the only work not derived from Dave Arneson's original campaign notes. A fifth installment, DA5 "City of Blackmoor", was announced but was never written or published.
Though there were no further direct explorations of Blackmoor, later Mystara products continued to make reference to it. For instance, "The Wrath of the Immortals", an epic adventure which described a massive war involving both heaven and earth, climaxes with the discovery of the preserved control room from the starship which had crashed near Blackmoor millennia ago.
There is also an ongoing Massively Multiplayer Role Playing Game (MMRPG) campaign, mmrpg.zeitgeistgames.com, organized by Zeitgeist games, which is similar in form to the Living Campaigns organized by the RPGA.
Megacon is Blackmoor's home convention, where the new season is kicked off each year.