Ancillary Justice is a science fiction novel by the American writer Ann Leckie, published in 2013. It is her debut novel and the first in her Imperial Radch space opera trilogy. The novel follows Breq—who is both the sole survivor of a starship destroyed by treachery and the vessel of that ship’s artificial consciousness—as she seeks revenge against the ruler of her civilization.

Ancillary Justice received critical praise and won the Hugo Award, the Nebula Award, the BSFA Award, the Arthur C. Clarke Award, and the Locus Award for Best First Novel. It is the only novel to have won the Hugo, Nebula, and Arthur C. Clarke awards.

Ancillary Justice is thousands of years in the future in which the principal power in human space is the expansionist Radch empire. The empire uses spaceships controlled by AIs, who control human bodies to use as soldiers.

The Radchaai do not distinguish people by gender, which Leckie “translates” into English by using “she” pronouns for everybody. The Radchaai main character must guess, frequently incorrectly, when she has to use languages with gender-specific pronouns.