A fan convention, or con (term antedates 1942 ), is an event in which fans of a particular film, television series, comic book, actor, or an entire genre of entertainment such as science fiction or anime and manga, gather to participate and hold programs and other events, and to meet experts, famous personalities, and each other. Some also incorporate commercial activity.

Fan conventions are traditionally organized by fans on a not-for-profit basis, though some events catering to fans may be run by commercial interests, either for profit or as part of a promotional program.

Actors often give out free autographs to the fans, perhaps in exchange for a flat appearance fee, and sometimes may perform songs that have no relevance to the shows to entertain the fans. Commercial conventions are usually quite expensive and are hosted in hotels. There is often tight security for the celebrities to protect against potentially fanatic fans. (Such features are not common at traditional science-fiction conventions, which are more oriented toward science fiction as a mode of literature, rather than toward visual media, and do not include any paid appearances by famous personalities.)

Many conventions have award presentations relating to their genre (such as the Hugo Awards which have been presented at The World Science Fiction Convention (WorldCon) since 1953). The largest fan convention was held at the Von Braun Center in 1993 for Star Trek with over 60,000 fans.

Anime conventions, gaming conventions, filk-music conventions and furry conventions may all be considered derivatives of science-fiction conventions, which began in the late 1930s.

From anime conventions has arisen the widespread stereotype of the fans' tendency to dress up as their favorite characters in elaborate costumes (known as cosplay in anime terminology) that are time-consuming and/or expensive to assemble. Conversely, while the wearing of costumes — and even a costume competition (known in the United States as a "masquerade") — has been an occasional feature of traditional science-fiction conventions since Forrest J Ackerman wore one during the First World Science Fiction Convention in 1939, this has never been the dominant feature of such events.