Set in the year 2517, after humans have arrived at a new star system, Firefly follows the adventures of the renegade crew of Serenity, a Firefly-class spaceship. The crew of Serenity fought on the losing side of a civil war and now try to survive on the outskirts of the society. The show also details a pioneer culture, the "Settlers", that exists on the fringes of the star system. In the Firefly universe the two surviving superpowers on Earth, the United States and China, fused to form the central federal government, called the Alliance.

Despite the series' short run, strong DVD sales and fan support resulted in the making of the spinoff film Serenity set two months after the events of the television show's final episode.

Firefly and Serenity have generated a devoted worldwide fanbase - members of which refer to themselves as "Browncoats". Browncoats have helped to sustain Firefly's legacy through comic books, fan fiction, role-playing games, podcasts, self-produced films, conventions and charity screenings.