Arkham Horror is a cooperative adventure board game designed by Richard Launius, originally published in 1987 by Chaosium. The game is based on Chaosium's roleplaying game Call of Cthulhu, which is set in the Cthulhu mythos of H.P. Lovecraft and other horror writers. The game's second edition was released by Fantasy Flight Games in 2005, with a third edition in 2018.

The game board is set in Lovecraft's fictional Massachusetts town of Arkham in 1926. Street, building and outdoor locations are featured. Gates to other planes open throughout the town (represented by tokens placed on the board.) Players take on the role of investigators, represented by a character card. Each investigator has several attributes (such as "sanity"), and cards representing items, spells, and other things. The investigators travel through the city, avoiding or fighting the monsters that enter through the gates, visiting city locations to acquire tools, and ultimately entering the gates.

After traveling to the other world and returning, the investigator can try to close the gate. While exploring city locations or other worlds, the investigators face random events which may benefit or harm them. As gates open, a "Doom Track" advances; if the track reaches its end, a powerful horrific creature known as the Ancient One breaks through into Arkham. In the 1987 edition of the game, this ends the game, and all players lose. In the second edition, when the doom track fills, this typically begins a final opportunity for the players to directly defeat the creature and win; otherwise they lose.