The Hostage of Zir is a science fiction novel by American writer L. Sprague de Camp, the seventh book of his Viagens Interplanetarias series and the fifth of its subseries of stories set on the fictional planet Krishna. Chronologically it is the third Krishna novel. It was first published in hardcover by Berkley/Putnam in 1977, and in paperback by Berkley Books in 1978. A new paperback edition was published by Ace Books in 1982 as part of the standard edition of the Krishna novels. An e-book edition was published by Gollancz's SF Gateway imprint on September 29, 2011 as part of a general release of de Camp's works in electronic form. The novel has also been translated into German and Czech.

The Viagens Interplanetarias series is a sequence of science fiction stories by L. Sprague de Camp, begun in the late 1940s and written under the influence of contemporary space opera and sword and planet stories, particularly Edgar Rice Burroughs's Martian novels. Set in the future in the 21st and 22nd centuries, the series is named for the quasi-public Terran agency portrayed as monopolizing interstellar travel, the Brazilian-dominated Viagens Interplanetarias. It is also known as the Krishna series, as the majority of the stories belong to a sequence set on a fictional planet of that name. While de Camp started out as a science fiction writer and his early reputation was based on his short stories in the genre, the Viagens tales represent his only extended science fiction series.