"In this intricately plotted novel of interplanetary intrigue, Heinlein is at his best."
- St. Louis Post Dispatch
"Pleasant and exciting reading."
- Galaxy Science-Fiction
"Bears the Heinlein cache of credible authenticity."
- Anthony Boucher (Fantasy and Science-Fiction)
"Not only America's premier writer of speculative fiction, but the greatest writer of such fiction in the world."
- Stephen King
"There is no other writer whose work has exhilarated me as often and to such an extent as Heinlein."
- Dean Koontz
"One of the most influential writers in American Literature."
- The New York Times Book Review