Fanfiction is defined as stories set in worlds or using characters created by other authors. The fans write to fill the gaps in original texts, contin-ue familiar stories, or create alternative universes. Most fanfiction is writ-ten within fandom, that is, communities of fans gathering around given works of fiction. Fandom is a subculture whose existence is based on other people's creations; the members take their creations, and use them to cre-ate their own artifacts, as well as build group traditions. The fans rewrite source texts to adapt them to their own needs; they actively participate in culture, and create their own art. Fandom creativity can take different shapes and forms. Apart from works of fiction, one can find examples of visual arts (“fanart”), music (“filk”), and audiovisual arts (“fanvid”). Re-gardless of form, all fandom's creations are based on the source text, which is usually refered to as “canon”. Canon is what binds fans as a group, giv-ing them creative space within which they can act. In a way, canon is the source of group identity, since most fans identify with the groups within which they create. Saying: “I'm a Star Trek fan” means declaring oneself as a member of a group that has its unique traditions, different, for exam-ple, of those cultivated by Harry Potter fans – although, of course, there are many elements that both groups share.