Science fiction fandom or SF fandom is a community or fandom of people interested in science fiction in contact with one another based upon that interest. SF fandom has a life of its own, but not much in the way of formal organization.

A fan or fanatic, sometimes also termed an aficionado or enthusiast, is a person who exhibits strong interest or admiration for something or somebody, such as a celebrity, a sport, a sports team, a genre, a politician, a book, a movie, a video game or an entertainer. Collectively, the fans of a particular object or person constitute its fanbase or fandom. They may show their enthusiasm in a variety of ways, such as by promoting the object of their interest, being members of a related fan club, holding or participating in fan conventions or writing fan mail. They may also engage in creative activities such as creating fanzines, writing fan fiction, making memes or drawing fan art.