"Unity" is the 17th episode of the third season of the American science fiction television series Star Trek: Voyager, the 59th episode overall. The episode first aired on the UPN network on February 12, 1997, as part of sweeps week. It was written by producer Kenneth Biller, and is the second episode to be directed by cast member Robert Duncan McNeill. It marked the first major appearance of the Borg in Voyager, which were kicked off with a teaser ending in the prior episode.

Set in the 24th century, the series follows the adventures of the Starfleet and Maquis crew of the starship USS Voyager after they were stranded in the Delta Quadrant far from the rest of the Federation. In this episode, while on an away mission, Chakotay is taken in by a group of former Borg who seek help from the crew of Voyager to reactivate their neural link. The ex-Borg force Chakotay to reactivate a Borg cube (a large Borg spaceship), but, in their new-found "Co-operative", the ex-Borg make the cube self-destruct, saving Voyager.

Biller was influenced by the story of the Tower of Babel in writing the episode, and also considered the dissolution of the Soviet Union to be an influence. The crew re-used the make-up and costumes of the Borg designed for the film Star Trek: First Contact, but sets were not re-used. A new fully computer generated Borg cube was created for "Unity", and the storyline of the episode was intended as a hint to those in the later two-part episode "Scorpion". According to Nielsen ratings, it received a 5.4/8 percent share of the audience on first broadcast. "Unity" was received positively by critics, with praise directed at McNeill's direction as well as Biller's plot.

Commander Chakotay (Robert Beltran) and Ensign Kaplan (Susan Patterson) hear a distress call while scouting ahead for Voyager in a shuttlecraft. They land the vessel but come under fire from hostile aliens, killing Kaplan and injuring Chakotay. He wakes in a room with a woman called Riley Frazier (Lori Hallier). She informs him that she is part of a group of survivors on the planet from a variety of races. There are other groups nearby, including those that attacked him. She calls her group a "Co-operative".

Meanwhile, the USS Voyager discovers a derelict Borg cube and Captain Kathryn Janeway (Kate Mulgrew) decides that an investigation is required in order to learn more about the Borg's technology. An away team boards the cube, discovering that either an accident or another species disabled the vessel. They take a Borg drone back onto Voyager, where the Doctor (Robert Picardo) accidentally revives it.

After being told by Frazier to remain where he is, Chakotay breaks out of his room where he sees that all the people around him on the alien planet possess Borg implant technology in their bodies. Frazier explains that an electro-kinetic storm broke their link with the Borg hive mind. Instead, the separated drones settled on a nearby planet. Because the connection between them was deactivated, different groups soon started fighting each other over the planet's limited resources. As Chakotay's health gets worse, the ex-Borg offer to connect him to a joint mind to heal his injuries, and he reluctantly accepts. Once part of the hive mind, he sees a montage of their memories. The ex-Borg remove the connection device as soon as Chakotay's health improves, however a residual telepathic link lingers and allows Chakotay and Frazier to get closer.

After Voyager arrives, Frazier and her group want Janeway to re-activate the neuroelectric generator on the damaged cube to extend a new joint mind across the entire planet, in order to stop the infighting. Chakotay pleads their case, but Janeway decides not to help them. As Chakotay returns to Voyager on board a shuttle, the Co-operative are attacked by hostile groups and use their telepathic link to force him to travel to the Borg cube, with Voyager in pursuit. Both Chakotay and an away team board the cube, and despite a firefight, he manages to reactivate the generator. This creates the new joint mind as expected, but also activates the cube, which begins powering up to attack Voyager. Chakotay and the away team are beamed back to Voyager as the Co-operative trigger the cube's self-destruct before it can endanger the Federation ship. The planet's inhabitants thank Voyager, but as a result of their actions, Chakotay later questions the morality of the Co-operative's motives with Janeway, as it connected many of the former Borg together in a new hive mind without consulting them.

The producers had wanted to bring the Borg into Voyager, which resulted in numerous pitches from a variety of writers. There were concerns from some of the crew that the events of the film Star Trek: First Contact effectively destroyed the Borg, but executive producer Rick Berman clarified both that the death of the Borg Queen in the film did not mean the destruction of the entire collective and that there were other Borg remaining in the Delta Quadrant. The alien race had made their first appearance in the Star Trek: The Next Generation episode "Q Who" and, at the time of the original broadcast of "Unity", had recently appeared in First Contact. The idea of Borg being separated from the collective had previously been seen in the episode of The Next Generation entitled "I, Borg" with the resultant effect seen in the two-part "Descent". "Unity" was written by producer Kenneth Biller, with the final version of the script being submitted on November 7, 1996. Though the film had not been released at the time he drafted the episode, Biller had read the First Contact script before writing the "Unity" script.