In the Star Trek fictional universe, the Borg cube ship is a variety of immense, cubic starship that functions as part of the Borg Collective. It was first seen in the Next Generation episode "Q Who?" at the collective's 2365 first contact with the United Federation of Planets. The cube appears to be the principal spacefaring unit of the collective, by far the Borg craft most often seen on screen and the type of vessel used in both the Battles of Wolf 359 and Sector 001. Cubes are popularly believed to number in the millions or greater; however, the three currently known cube identification numbers, 461, 630, and 1184, seem to indicate smaller numbers. These ships' low numbers may be coincidence, however, or these may not be the ships' complete registries.

The design of a Borg cube is determined by the materials at hand and what is currently needed in a ship. The only unifying principles of design are a roughly cubical shape, a decentralized organization, and a size of several thousand meters per edge. Common capabilities of cubes include high warp capabilities, self-regeneration (at least of the outermost layer), beam weapons, and accommodation of Borg cybernetic units numbering in the tens or hundreds of thousands. Cubes have been known to carry Borg sphere ships in cavities covered by large slide-away hatches in their outermost layers, however it is not known if this is common.

Two basic styles of cube have been seen: the first, seen in The Next Generation, had an outer layer composed of a thin framework, allowing a green glow to emanate from within; the second, seen in Star Trek: Voyager, has a more solid_looking exterior, and less of a noticeable inner light, possibly indicative of a new assimilated technology or a new tendency to employ physical armor in protecting cubes.

Another type of cube, the tactical cube, was seen in a late season of Voyager: a model specifically designed for battle, which employed large, solid armor plates to protect itself.