Star Trek VI: The Undiscovered Country is the sixth feature film in the Star Trek science fiction franchise and is the last of the Star Trek films to include the entire main cast of the 1960s Star Trek television series. It was released in 1991 by Paramount Pictures. It was directed by Nicholas Meyer and written by Meyer with Denny Martin Flinn. After an ecological disaster leads to two longstanding enemies—the Federation and the Klingon Empire—brokering a tenuous truce, the crew of the USS Enterprise must prevent war from breaking out on the eve of universal peace.

The Undiscovered Country was initially planned as a prequel to the original series, with younger actors portraying the crew of the Enterprise while attending Starfleet Academy, but the idea was discarded because of negative reaction from the cast and the fans. This idea was later used to create the 2009 film, Star Trek. Faced with producing a new film in time for Star Trek's 25th anniversary, Flinn and Meyer, the director of Star Trek II: The Wrath of Khan, wrote a script based on a suggestion from Leonard Nimoy about what would happen if "the wall came down in space", touching on the contemporary events of the Cold War.

Principal photography took place between April and September 1991. The production budget was smaller than anticipated because of the critical and commercial failure of Star Trek V: The Final Frontier. Because of a lack of sound stage space on the Paramount Pictures lots, many scenes were filmed around Hollywood. Meyer and cinematographer Hiro Narita aimed for a darker and more dramatic mood, subtly altering redresses of sets originally used for the television series Star Trek: The Next Generation. Producer Steven-Charles Jaffe led a second unit that filmed on an Alaskan glacier that stood in for an alien gulag. Cliff Eidelman produced the film's score, which is intentionally darker than any previous Star Trek offering.

The film was released in North America on December 6, 1991. The Undiscovered Country garnered positive reviews, with publications praising the lighthearted acting and facetious references. The film performed strongly at the box office; it posted the largest opening weekend gross of the series before going on to earn $96,888,996 worldwide. The film earned two Academy Award nominations, for Best Makeup and Best Sound Effects, and is the only Star Trek movie to win a Saturn Award for Best Science Fiction Film. A special collectors' edition DVD version of the film was released in 2004, for which Meyer made minor alterations to his cut of the movie. Star Trek creator Gene Roddenberry died shortly before the movie's premiere, just days after viewing the film.