"Regeneration" is the forty-ninth episode of the American science fiction television series Star Trek: Enterprise, the twenty-third episode of the second season. It first aired on May 7, 2003, on the UPN in the United States. The episode was written by Mike Sussman and Phyllis Strong, and was directed by David Livingston. It was a follow-up to the feature film Star Trek: First Contact.

Set in the 22nd century, the series follows the adventures of the first Starfleet starship Enterprise, registration NX-01. In this episode, a research team in the Arctic inadvertently triggers the reanimation of several cybernetically enhanced aliens, killed in apparent spacecraft crash over a hundred years earlier. The aliens assimilate the researchers before escaping into space. The Enterprise pursues the ship and is attacked, forcing Archer to destroy the vessel. Afterwards they discover that the aliens sent a message into the Delta Quadrant containing the coordinates of Earth, a message that will not arrive until the 24th century.

The episode used props and costumes from previous Star Trek series in order to represent the Borg. The guest cast included Bonita Friedericy, the wife of main cast member John Billingsley. The ratings received by the episode were similar to those received during the previous week, and the number of viewers were one of the highest for the year. The critical response to "Regeneration" was mixed, with concerns directed at potential continuity problems, and that the appearance of the Borg was a little obvious. A follow-up episode to "Regeneration" was pitched for the fifth season of Star Trek: Enterprise but the show was cancelled at the end of the fourth season.