Seven of Nine (born Annika Hansen) is a fictional character introduced in the American science fiction television series Star Trek: Voyager. Portrayed by Jeri Ryan, she is a former Borg drone who joins the crew of the Federation starship Voyager. Her full Borg designation was Seven of Nine, Tertiary Adjunct of Unimatrix Zero One. While her birth name became known to her crewmates, after joining the Voyager crew she chose to continue to be called Seven of Nine, though she allowed "Seven" to be used informally.

Seven of Nine was introduced in the fourth-season premiere, "Scorpion, Part II". The character replaced Kes in the main cast, and was intended to introduce a foil to Captain Kathryn Janeway, similar to the role Spock performs for Captain Kirk in Star Trek: The Original Series. The character appeared through the final episode, "Endgame". Stories related to her relationship with Captain Janeway and with The Doctor appeared throughout the series; some episodes, such as "The Raven", explored her background and earlier life as Annika Hansen before she was assimilated by the Borg.

Seven of Nine, again played by Ryan, also appears in the series Star Trek: Picard as a recurring character in the first season before being promoted to series regular for the second and third seasons.