Bramscher, Paul. "Clifford Simak's Biography". Paul Bramscher. Diarsipkan dari asli tanggal 2011-05-23. Diakses tanggal 2017-03-19. (archive.org link)
(Inggris)Clifford D. Simak di Internet Speculative Fiction Database (ISFDB). Retrieved 2013-04-05. Select a title to see its linked publication history and general information. Select a particular edition (title) for more data at that level, such as a front cover image or linked contents.
