Defiance is an American science fiction Western drama television series developed by Rockne S. O'Bannon, Kevin Murphy, and Michael Taylor; the series is produced by Universal Cable Productions.

The show takes place in a post-apocalyptic future on a radically transformed Earth containing new species, some having arrived from space, many others the result of haphazard contamination by the terraforming technology used by the alien race the Votans, which has transformed native flora and fauna in unforeseen ways. The story begins in the year 2046 when Earth has been considerably changed, with new topography, the extinction of plant and animal species and the emergence of new species. The series follows Joshua Nolan (Grant Bowler), his adopted alien daughter Irisa (Stephanie Leonidas), and the town's new mayor, Amanda Rosewater (Julie Benz), in addition to an ensemble of actors portraying different characters in the growing town in the city-state of Defiance, built on the ruins of St. Louis.

The series was broadcast in the United States on the cable channel Syfy and in various international markets. It premiered on April 15, 2013, in the United States and that same week in most countries that picked up the series. Defiance was renewed for a 13 episode third season on September 25, 2014, which premiered on June 12, 2015.

On October 16, 2015, the show was cancelled by Syfy, citing financial reasons after having completed its third season. However, the companion video game, Defiance, continued to be supported until April 2021 when all servers and community services were shut down. On March 1, 2016, Trion Worlds announced a major update for the game, promoted as season four of the show. They also stated they had no plans of making a sequel, instead they will continue to update the game with new content. The new version, titled Defiance 2050, was released on July 10, 2018, for PC, Xbox One, and PlayStation 4, and recreates the original game (set in 2046) into the year 2050, 20 years after the Human-Votan war-ending Arkfall event.