Spelljammer is a campaign setting originally published for the Advanced Dungeons & Dragons role-playing game, which features a fantastic outer space environment. Subsequent editions have included Spelljammer content; a Dungeons & Dragons 5th edition setting update was released on August 16, 2022.

The planes of the Dungeons & Dragons roleplaying game constitute the multiverse in which the game takes place. Each plane is a universe with its own rules with regard to gravity, geography, magic and morality. There have been various official cosmologies over the course of the different editions of the game; these cosmologies describe the structure of the standard Dungeons & Dragons multiverse.