A Trekkie (or Trekker) is a self-described term for a fan of the Star Trek science fiction franchise. Not all "Trekkies" are created equal, however, with some having distinct preferences for The Original Series, The Next Generation, Deep Space Nine, or Voyager. Some are also fans of the Pocket Books tie-in novel franchise.

Some Trekkers regularly attend Star Trek Convention s (called "cons"), and are sometimes bitter rivals of hard core Star Wars fans. By analogy, Star Wars fans sometimes refer to themselves as "Warsies," and Mystery Science Theater 3000 fans frequently refer to themselves as "MSTies"

The term Trekkie is sometimes considered derogatory, perhaps because of a perceived parallel to the term groupie. Some Star Trek enthusiasts prefer the term Trekker, while some others hold the latter term to be stupid and, for that reason, self-identify as Trekkies. Some Trekkies even say that Trekker is a Trekkie who is embarrassed for being Trekkie.

There are many Star Trek fan clubs, the largest currently being STARFLEET International which has about 4,000 members.

A 1997 documentary film, called Trekkies, chronicled some of these devoted fans.

There is a persistent stereotype that amongst Trekkies can be found speakers of the artificial Klingon language. The reality is less clear-cut, as some of its most fluent speakers are more language aficionados than people obsessed with Star Trek. Most Trekkies have no more than a basic vocabulary of Klingon, like a few common words heard over the series innumerable times, but not Klingon's syntax or precise phonetics.

Trekkies have been parodied in several films including Galaxy Quest. William Shatner did a famous sketch on Saturday Night Live that also parodied Trekkies in which he played himself at a Star Trek convention at which he told the Trekkies to "get a life". There was once a pitch for a reality TV show featuring a group of "die hard" Trekkies and one normal person, though it remains to be seen if such an episode will be aired.

Note: The first people to call themselves Trekkies were writers of Slash fiction (Kirk/Spock).