Demons of the Deep is a single-player roleplaying gamebook written by Steve Jackson (the American game-designer, rather than the series co-creator), illustrated by Duncan Smith and originally published in 1986 by Puffin Books.

Demons of the Deep is the only gamebook of those that the American Steve Jackson wrote that follows a traditional linear design.

The player sinks into the sea but, thanks to magic, does not drown, beginning an adventure in an ancient domain sunken beneath the waves.

The player-character must collect black pearls and learn a spell to form skeletons from them, then use these to attack and defeat the pirate crew of the Troll.

The book takes place almost entirely underwater, in Atlantis, a sunken continent located west of Allansia.