Gems are an extraterrestrial species of "magical" beings that play a key role in Steven Universe. Gems are an intergalactic race which 5,750 years ago maintained several outposts on Earth, with plans to completely colonize the planet, but were driven off by Rose Quartz's rebellion, leaving the Crystal Gems, and the Corrupted Gems, the only Gems on the planet, except for a small group of stranded Gems from the Gem Homeworld.

While generally humanoid, gems have their namesake gemstones visible somewhere on their bodies and may have multiples of certain body parts. Furthermore, while they can shapeshift, their transformations keep their normal color palette.