"E²" (pronounced "E-Squared") is the seventy-third episode of the American science fiction television series Star Trek: Enterprise, the twenty-first episode of season three. It first aired on May 5, 2004, on the UPN network in the United States. The episode was the fifth of the season written by Mike Sussman, and it was directed by Star Trek: Voyager alumnus Roxann Dawson, her fourth of the third season.