"Assignment: Earth" is the twenty-sixth and final episode of the second season of the American science fiction television series Star Trek. Written by Art Wallace (based on a story by Wallace and Gene Roddenberry) and directed by Marc Daniels, it was first broadcast on 29 March 1968. In the episode, engaged in "historical research", the USS Enterprise travels back through time to 1968 Earth, where they encounter an interstellar agent planning to intervene in 20th-century events. Kirk and Spock are uncertain of his motives.