Ethan of Athos is a 1986 science fiction novel by American author Lois McMaster Bujold. The title character is Dr. Ethan Urquhart, Chief of Biology at the Sevarin District Reproduction Centre on the planet Athos, who is sent to find out what happened to a shipment of vital ovarian tissue cultures. Set in the fictional universe of Bujold's Vorkosigan Saga, the novel mentions but does not feature her usual protagonist Miles Vorkosigan. To date, Bujold has never revisited the settings of Athos or Kline Station in her many subsequent novels, but the events of Ethan of Athos are later referred to indirectly in the novels Borders of Infinity (1989) and Cetaganda (1995).

Bujold had written her first novel Shards of Honor and its sequel The Warrior's Apprentice — both unpublished — when she wrote Ethan of Athos, a standalone work that was purposely short "because the current cargo-cult rumor amongst the wanna-be-published back then was that editors would be more likely to read a short manuscript." All three novels were subsequently sold, and published in 1986.

Bujold named Athos, a planet founded and maintained as an exclusively male-populated colony with a planetary religion and ideology supporting this single-sex structure, after the Greek Mount Athos, which has prohibited the entry of women for religious reasons since even before the ban was officially proclaimed by the Byzantine emperor Constantine Monomachos in 1046.

Ethan of Athos has been reprinted several times, and appeared in the 2001 Bujold omnibus Miles, Mystery and Mayhem alongside Cetaganda and the novella "Labyrinth". The novel was released on audio cassette in September 1999 narrated by Michael Hanson and Carol Cowan, and as a digital audiobook in March 2009 narrated by Grover Gardner.