Firefly is an American space Western drama television series, created by writer and director Joss Whedon, under his Mutant Enemy Productions label. Whedon served as an executive producer, along with Tim Minear. The series is set in the year 2517, after the arrival of humans in a new star system, and follows the adventures of the renegade crew of Serenity, a "Firefly-class" spaceship. The ensemble cast portrays the nine characters living aboard Serenity. Whedon pitched the show as "nine people looking into the blackness of space and seeing nine different things."

The show explores the lives of a group of people, some of whom fought on the losing side of a civil war, who make a living on the fringes of society as part of their star system's pioneer culture. The two surviving superpowers, the United States and China, united to form the central federal government, called the Alliance. According to Whedon's vision, "Nothing will change in the future: Technology will advance, but we will still have the same political, moral, and ethical problems as today."

Firefly premiered in the United States on the Fox network on September 20, 2002. By mid-December, it had averaged 4.7 million viewers per episode and was 98th in Nielsen ratings. It was canceled after 11 of the 14 produced episodes were aired. Despite its short run, it received strong sales when it was released on DVD and has large fan support campaigns. It won a Primetime Emmy Award in 2003 for Outstanding Special Visual Effects for a Series. TV Guide ranked it No. 5 on their 2013 list of 60 "shows that were canceled too soon".

The show's post-airing success led Whedon and Universal Pictures to produce Serenity, a 2005 film that continues the story from the series. The Firefly franchise expanded into other media, including comics and two tabletop role-playing games.