Mission to Horatius is a novel based on the American science fiction television series Star Trek: The Original Series. It was published in 1968 by Whitman, and was the first original novel based on the series; the first novel for adult audiences, Spock Must Die!, was not published until February 1970. Mission to Horatius details the adventures of the crew of the U.S.S. Enterprise investigating where a distress signal had originated, resulting in them engaging with several different human colonies.

Spock Must Die! is an American science fiction novel written by James Blish, published February 1970 by Bantam Books. It was the first original novel based on the Star Trek television series intended for adult readers. It was preceded by a tie-in comic book line published by Gold Key and the novel Mission to Horatius by Mack Reynolds, all intended for younger readers.