"Tomorrow Is Yesterday" is a first season episode of the original science fiction television series, Star Trek. It is episode #19, production #21, first broadcast on 26 January 1967, repeated 13 July 1967, and was remastered in 2006 for syndication broadcast on 5 May 2007. The teleplay was written by D.C. Fontana and directed by Michael O'Herlihy. In the plot, the crew of the USS Enterprise travels back to 1968 Earth and must correct damage they caused to the timeline.