Two of de Camp's friends and colleagues, science fiction writers Robert A. Heinlein and Isaac Asimov, with whom he had worked on military research during World War II, were involved in the book in different ways. It features a laudatory introduction by Heinlein and is dedicated to Asimov, whom de Camp stated "helped to push this one over the hump." Asimov recorded some vivid impressions of the author's research for the book in his own introduction to de Camp's short story collection "The Continent Makers and Other Tales of the Viagens" (1953).