Oneiromancy is a form of divination based upon dreams; it is a system of dream interpretation that uses dreams to predict the future.

Dreams occur throughout the Bible as omens or messages from God:

• Jacob dreams of a ladder to heaven (Genesis 28);
• his son Joseph dreamed of his future success (Genesis 37) and intrepreted the dreams of the Pharaoh of Egypt (Genesis 41);
• Solomon conversed with God in his dreams;
• Daniel interpreted dreams (in the Book of Daniel);
• Joseph, husband of Mary, was directed to flee to Egypt (Matthew 2);
• Paul was told to go to Macedonia (Acts 16).

Aristotle and Plato both discuss dreams in various works. Artemidorus gives a list of authors mentioned in his Oneirocritica, the longest of the ancient dreambooks. All of the referenced works are lost, but fragments are preserved in Artemidorus and other ancient authors. Achmet wrote an edition of Artemidorus Oneirocritica in addition to his own. Astrampsychus was the pseudonymous author of a number of divinatory, magical and medical works, including an Oneirocriticon.

Oneiromancy is also used as a type of magic in the Dungeons & Dragons game, which influences, interprets or alters dreams, and also has an effect on the fictional Plane of Dreams, or Dreamscape.