- Name's the Same: Both this and Falling Skies feature invading aliens called "Overlords". The invasions are very different, though.
- Old Shame: Clarke mentions in the Millennial edition that he wrote this when he still had a belief in the paranormal.
- At least one edition of the book includes the extremely unusual disclaimer "The ideas expressed in this novel are not those of the author."
- Shout-Out: The Peter Gabriel-era Genesis song "Watcher of the Skies" is based on/inspired by this novel.
Trivia / Childhood's End