The Urantia Book is a spiritual, philosophical, and religious book that originated in Chicago, Illinois, United States sometime between 1924 and 1955, claimed, when first published, to have been written by celestial beings. The actual authorship remains a matter of debate, though it has been noted that it appears to have plagiarized multiple sources, without attribution. It received various degrees of interest ranging from praise to criticism for its religious and science-related content, its unusual length, and the unusual names and origins of the authors named within the book.

William Samuel Sadler was an American surgeon, self-trained psychiatrist, and author who helped publish The Urantia Book. The book is said to have resulted from Sadler's relationship with a man through whom he believed celestial beings spoke at night. It drew a following of people who studied its teachings.