The Borg are an alien group that appear as recurring antagonists in the Star Trek fictional universe. The Borg are cybernetic organisms (cyborgs) linked in a hive mind called "the Collective". The Borg co-opt the technology and knowledge of other alien species to the Collective through the process of "assimilation": forcibly transforming individual beings into "drones" by injecting nanoprobes into their bodies and surgically augmenting them with cybernetic components. The Borg's ultimate goal is "achieving perfection".

Aside from being recurring antagonists in the Next Generation television series, they are depicted as the main threat in the film Star Trek: First Contact. In addition, they played major roles in the Voyager and Picard series.

The Borg have become a symbol in popular culture for any juggernaut against which "resistance is futile", a common phrase uttered by the Borg.