Mystery Science Theater 3000 (abbreviated as MST3K) is an American science fiction comedy television series created by Joel Hodgson. The show premiered on KTMA-TV (now WUCW) in Minneapolis, Minnesota, on November 24, 1988. It then moved to nationwide broadcast, first on The Comedy Channel for two seasons, then Comedy Central for five seasons until its cancellation in 1996. Thereafter, it was picked up by The Sci-Fi Channel and aired for three more seasons until another cancellation in August 1999. A 60-episode syndication package titled The Mystery Science Theater Hour was produced in 1993 and broadcast on Comedy Central and syndicated to TV stations in 1995. In 2015, Hodgson led a crowdfunded revival of the series with 14 episodes in its eleventh season, first released on Netflix on April 14, 2017, with another six-episode season following on November 22, 2018. A second successful crowdfunding effort in 2021 produced 13 additional episodes shown on the Gizmoplex, an online platform that Hodgson developed which launched in March 2022. As of 2023, 230 episodes and a feature film had been produced as well as three live tours.

The show initially starred Hodgson as Joel Robinson, a janitor trapped by two mad scientists ("The Mads") on the Earth-orbiting Satellite of Love and forced to watch a series of B movies to monitor his reaction to them. To keep his sanity, Joel crafts sentient robot companions, including Tom Servo, Crow T. Robot, Cambot and Gypsy, to keep him company and help him humorously comment on each movie as it plays, a process known as riffing. Each two-hour episode would feature a single movie (often edited for time constraints), sometimes preceded by various old shorts and educational films, with Joel, Tom, and Crow watching in silhouette from a row of theater seats at the bottom of the screen. These "theater segments" were framed with interstitial sketches called "host segments". The show's cast changed over its duration; most notably, the character of Joel was replaced by Mike Nelson (played by Michael J. Nelson) halfway through the show's fifth season. Other cast members, most of whom were also writers for the show, include Trace Beaulieu, Josh Weinstein, Jim Mallon, Kevin Murphy, Frank Conniff, Mary Jo Pehl, Bill Corbett, Paul Chaplin, and Bridget Jones Nelson. The 2017 revival features a primarily new cast, including Jonah Ray who plays the new human test subject Jonah Heston, along with Felicia Day and Patton Oswalt as "The Mads" and Baron Vaughn, Hampton Yount, and Rebecca Hanson voicing Tom Servo, Crow T. Robot, and Gypsy, respectively. Season 13 brought back this cast while integrating Emily Connor, played by Emily Marsh, and others from the live tours in this era.

Initially MST3K did not garner high viewership numbers, but the show's popularity spread through online word-of-mouth by its fans known as "MSTies" or "Mysties" (who would remind others to "Keep circulating the tapes"), frequent repeats, syndication, and home media offerings produced by Rhino Entertainment. Currently, this popularity continues through Shout! Studios, who along with Hodgson, now own the rights to the show and supported the revived series. MST3K was listed as one of Time magazine's "100 Best TV Shows of All-TIME" in 2007, and TV Guide has noted MST3K as one of the top cult television shows. The show won a Peabody Award in 1993, was also nominated for two Emmy Awards in 1994 and 1995, and for the CableACE Award from 1992 to 1997. The show was considered highly influential, contributing towards the practice of social television, and former cast members launched projects similarly on riffing on films, including The Film Crew, RiffTrax, and Cinematic Titanic. MST3K also brought to light several older movies that had fallen into obscurity or had received little or no public attention when originally released. Many of these films were subsequently identified as among the worst movies ever made, most notably Manos: The Hands of Fate.