In fantasy fiction, a lich (; from the Old English līċ, meaning "corpse") is a type of undead creature.

Various works of fantasy fiction, such as Clark Ashton Smith's "The Empire of the Necromancers" (1932), had used lich as a general term for any corpse, animated or inanimate, before the term's specific use in fantasy role-playing games. The more recent use of the term lich for a specific type of undead creature originates from the 1976 Dungeons & Dragons role-playing game booklet Greyhawk, written by Gary Gygax and Rob Kuntz.

Often such a creature is the result of a willful transformation, as a powerful wizard skilled in necromancy who seeks eternal life uses rare substances in a magical ritual to become undead. Unlike zombies, which are often depicted as mindless, liches are sapient revenants, retaining their previous intelligence and magical abilities. Liches are often depicted as holding power over lesser mindless undead soldiers and servants.

A lich's most often depicted distinguishing feature from other undead in fantasy fiction is the method of achieving immortality; liches give up their souls to form "soul-artifacts" (called a "soul gem", "phylactery" or "horcrux" in other fantasy works), the source of their magic and immortality. Many liches take precautions to hide and/or safeguard one or more soul-artifacts that anchor a part of a Lich's soul to the material world. If the corporeal body of a lich is killed, that portion of the lich's soul that had remained in the body does not pass on to the next world, but will rather exist in a non-corporeal form capable of being resurrected in the near future. However, if all of the lich's soul-artifacts are destroyed, then the lich's only anchor in the material world would be the corporal body, whereupon destruction will cause permanent death.