The Klyntar (colloquial: symbiotes) are a fictional species of extraterrestrial symbiotes appearing in American comic books published by Marvel Comics, most commonly in association with Spider-Man. The symbiotes form a symbiotic bond with their hosts, through which a single entity is created. They are able to alter their hosts' personalities and/or memories by influencing their darkest desires, along with amplifying their physical and emotional traits and personality and thereby granting them super-human abilities. There are more than 40 known symbiotes in the Marvel Universe.

The first and most well-known symbiote is Venom, who originally attached itself to Spider-Man during the 1985 Secret Wars miniseries. After Spider-Man rejected it upon discovering its true evil nature, the symbiote bonded with his rival, Eddie Brock, with whom it first became Venom. The character has since endured as one of Spider-Man's archenemies, though he has also been occasionally depicted as an antihero. Other characters have later merged with the Venom symbiote, including the villain Mac Gargan, and Flash Thompson, who became the superhero Agent Venom. Other well-known symbiotes are Carnage, an offspring of Venom who, when merged with its most infamous host, Cletus Kasady, has served as an enemy of both Spider-Man and Venom; and Anti-Venom, which originated when the Venom symbiote re-merged with Brock after a long split, gaining a new white appearance and additional powers as a result of Martin Li using his powers on Brock to cure his cancer.

Since their conception, the symbiotes have appeared in various media adaptations, including films, television series, and video games. Venom has been the most featured one, appearing in the 2007 film Spider-Man 3, and as the titular protagonist of the 2018 film Venom. Carnage also made its cinematic debut in the film Venom: Let There Be Carnage (2021).