Marcus may refer to:
- Marcus, serving aboard the USS Enterprise (NCC-1701-D)
- Alexander Marcus, father of Carol Marcus.
- Admiral Alexander Marcus, his alternate reality counterpart.
- Carol Marcus, one of the creation team for the Genesis Project, and a past love of James Kirk.
- Carol Marcus, her alternate reality counterpart.
- David Marcus, son of Carol Marcus and James Kirk.
- Claudius Marcus, a Roman of planet 892-IV.
- Claudius Marcus (gladiator), a gladiator from 892-IV.
- Admiral Marcus Holt, commander of Deep Space 3.
- Marcus II, Sten's homeworld.
- Marcos XII, the first planet which the evil angel-being Gorgan decided to conquer.
- Trula M. Marcus, an actress in DS9: "Shadowplay".
- Cindy Marcus, co-writer of DS9: "Profit and Loss".