The exact, detailed circumstances of the origin of The Urantia Book are unknown for two reasons. The human beings most directly involved in the transactions leading to the subsequent publication of The Urantia Book in 1955 took and honored what they described as a sacred promise of secrecy, and all are now deceased. The book is purportedly authored by numerous celestial personalities appointed to the task of providing an epochal revelation of religious significance to the human beings on our planet, referred to as “Urantia” in the book.  In the Foreword of The Urantia Book the purported purpose of the revelation is “to present enlarged concepts and advanced truths, in our endeavor to expand cosmic consciousness and enhance spiritual perception.”
In 1911, William S. Sadler and his wife Lena Sadler, both physicians living in Chicago, came into contact with a neighbor who was exhibiting unusual night time behavior including the expression of verbal communications asserting origination with celestial beings existing beyond the range of human perception. Increasingly over time, these communications became more detailed and included all of the information that was subsequently published in 1955 as The Urantia Book. 
Both Sadlers were respected physicians in their community. In addition, Dr William Sadler authored numerous books, including in 1929 The Mind at Mischief, in which he examined what he believed were fraudulent methods of mediumship, the paranormal and supernatural phenomena. Though known as a debunker of supernatural phenomena, he wrote in the appendix to The Mind at Mischief that there were two cases of claimed psychic phenomena for which he had no explanation.  The specific instance that referred to the communications that eventually became The Urantia Book was described this way:
“The other exception has to do with a rather peculiar case of psychic phenomena, one which I find myself unable to classify, and which I would like very much to narrate more fully; I cannot do so here, however, because of a promise which I feel under obligation to keep sacredly. In other words, I have promised not to publish this case during the lifetime of the individual. I hope sometime to secure a modification of that promise and be able to report this case more fully because of its interesting features. I was brought in contact with it, in the summer of 1911, and I have had it under my observation more or less ever since, having been present at probably 250 of the night sessions, many of which have been attended by a stenographer who made voluminous notes.
A thorough study of this case has convinced me that it is not one of ordinary trance. While the sleep seems to be quite of a natural order, it is very profound, and so far we have never been able to awaken the subject when in this state; but the body is never rigid, and the heart action is never modified, though respiration is sometimes markedly interfered with. This man is utterly unconscious, wholly oblivious to what takes place, and unless told about it subsequently, never knows that he has been used as a sort of clearing house for the coming and going of alleged extra-planetary personalities. In fact, he is more or less indifferent to the whole proceeding, and shows a surprising lack of interest in these affairs as they occur from time to time.
Eighteen years of study and careful investigation have failed to reveal the psychic origin of these messages. I find myself at the present time just where I was when I started. Psychoanalysis, hypnotism, intensive comparison, fail to show that the written or spoken messages of this individual have origin in his own mind. Much of the material secured through this subject is quite contrary to his habits of thought, to the way in which he has been taught, and to his entire philosophy. In fact, of much that we have secured, we have failed to find anything of its nature in existence. Its philosophic content is quite new, and we are unable to find where very much of it has ever found human expression...It is essentially Christian, and is, on the whole, entirely harmonious with the known scientific facts and truths of this age." 
In 1924, a group of Sadler's friends, former patients, and colleagues began meeting for Sunday intellectual discussions. This group, eventually known as the Forum, became interested in the neighbor’s communications when Sadler mentioned the unusual case and read samples of the information communicated. Over time, a message reportedly was received that this group would be allowed to devise questions and that answers would be given by celestial beings through the neighbor who was referred to only as the “contact personality.”
A smaller group of individuals referred to as the Contact Commission, including William and Lena Sadler, was responsible for gathering the questions from the Forum to be answered by the celestial personalities, acting as the custodians of the handwritten manuscripts that were compiled as a result of this process, and arranging for typing and proofreading the material. The Sadlers and the other members of the Contact Commission confirmed before their deaths that the information that comprised the papers of the book was communicated and transcribed from 1925 until 1935 with the first three parts completed in 1934 and the fourth in 1935.
The last official Forum gathering was in 1942. However, the communications purportedly continued for another two decades while members of the Forum studied the book in depth. According to Sadler and others, permission to publish The Urantia Book was given to them in 1955. Urantia Foundation was formed in 1950 as a tax-exempt educational society in Illinois, and through privately raised funds, the book was published under international copyright on October 12, 1955.
Dr. William S. Sadler died in 1963, pre-deceased by his wife, Lena. The identity of the Contact Personality does not appear in The Urantia Book and was never revealed by either the Sadlers or other members of the Contact Commission, the only persons who actually knew who he was. Notwithstanding speculative claims, to the contrary by Martin Gardner and other researchers, no factual evidence of his identity has ever been found and no person has ever come forward to claim such identity. 
The book has 2097 pages and contains 196 chapters divided into four parts. The book says that it is the most complete revelation from God so far available to humanity. 
Part I consists of 31 papers that address God as Creator of the universe and Father of all beings. Of all relation between eternal God and human, fatherly love is the most important: “God loves not like a father, but as a father”.  Then follows the description of Trinity, located in Paradise, which is the goal of destiny for mortals and other inhabitants of the universe. Described are numerous spiritual beings and their functions in the vast universe. The structure of the cosmos is also narrated as well as the organisation and celestial administration of galaxies, stars and planets.  The universe is teeming with life and contains myriads of inhabited worlds.  God, The Universal Father sent out a supreme mandate "Be you perfect, even as I am perfect". It is humankind first duty to strive for perfection. 
Part II is composed of 25 papers pertaining to the origin and administration of local universes - the units of vast creation subsequently divided into constellations and local systems of inhabited planets. We are living in the local universe Nebadon.  The Creator and Sovereign of our local universe is Michael of Nebadon who once sojourned on Earth as Jesus of Nazareth. In the life after death a man, after “a short and intense test during initial life of material existence”, continues his experience from this point where his life was finished on Earth. "The entire universe is one vast school." The Biblical “war in heaven” as the rebellion in local system of inhabited worlds is presented too. The physical aspects of local universe are also highlighted in this section. 
Part III includes 63 papers that compile a broad history of the Earth, the formation of planet and its geological chronicle, creation of life and its evolution from the first primitive cells to the appearance of human. The evolution is supervised by celestial intelligences according to God's plan. The book then describes the life of prehistoric man his institutions, habits, marriage and family; the origin of races and the sources of primitive religion. Presented is the story of very ancient Dalamatia and its teaching, the story of Garden of Eden and Adam and Eve; all of them appearing in the later traditions as gods that coming to Earth. Described are the sources and genesis of modern civilization, prehistory and history of Europe, America, Africa and Asia (Mesopotamia, Egypt, India and China). Narrated are the beginnings of many world religions and their founders: Ikhnaton, Moses, Buddha, Confucius, Lao-tse and Zoroaster. Old Testament times are unfolding in the story of Abraham, Melchizedek and the history of Israel.  Elucidate is the nature of religion and its role in human experience. The book attempts to synchronize religion, science and philosophy: “The ideal human estate is that in which philosophy, religion, and science are welded into a meaningful unity.” Introduced is the idea of Thought Adjuster as spiritual fragment of God in human and the work of Seraphic Planetary Government. Described are the new philosophical concepts of reality, time and eternity, Supreme Being and Absolutes.
More than one third of the content of the book (Part IV - 77 papers) is devoted to a narrative of the life and teachings of Jesus.  From his birth in Bethlehem and infancy in Alexandria, the story extends through his years of school in Nazareth and his work as a young carpenter after the death of his father Joseph, in order to sustain his widowed mother and eight brothers and sisters. Topics include a girl Rebecca who fell in love with him, and Jesus's rejection of her proposal for marriage. Jesus is said to have traveled around the Mediterranean Basin (Alexandria, Rome, Athens etc.) and regions of the Middle East (Mesopotamia and Caspian Sea region) in his late 20s, and after these trips, the narrative begins to parallel what is depicted in the New Testament, but with numerous extra details. John the Baptist and the twelve Apostles are people of flesh and blood with their virtues and flaws. Jesus' teachings, as presented to his apostles and followers, are exhaustive, enlarged and presented in contemporary language. The work of the Women's Evangelistic Corps appointed by Jesus is also narrated. 
Jesus' mission on Earth the book describes as the seventh bestowal of a Creator Son. Each Creator Son can rule his part of the universe – (termed the "local universe") – after completing seven bestowals, the final of them is in the likeness of mortal flesh. This is the one of reasons why the Creator Son came to Earth – Urantia. The other purpose of his mission is stated in the book: "A Creator Son did not incarnate in the likeness of mortal flesh and bestow himself upon the humanity of Urantia to reconcile an angry God but rather to win all mankind to the recognition of the Father's love and to the realization of their sonship with God." The core of Jesus' teaching is that men are children of God and their fellows are their brethren in one big family, when Jesus is their elder brother.  The idea of the kingdom of God as presented by Jesus is the spiritual rule of Heavenly Father in the hearts of men, but many of his followers misinterpret this idea as a purely earthly kingdom. The book states that today Christianity is rather a religion about Jesus instead religion of Jesus – his original teaching – which the book reinstates. 
The claim of revelation in The Urantia Book has been criticized for various reasons. Because the book does not support certain tenets of Christianity, such as the atonement doctrine, while at the same time presenting an account of parts of Jesus' life absent in the Bible, others with a Christian viewpoint have argued it cannot be genuine.  Gooch notes that while its "somewhat dated, elegant" prose could be read as fiction, due to its claim of divine inspiration "the book invites reactions far more scathing than [it] ... might otherwise merit."  Gooch says that for nonbelievers, the book is a mixture of being "fascinating, inspiring, compelling, haunting, entertaining, annoying, incomprehensible, and always wordy." 
Most of the criticism of The Urantia Book contains Martin Gardner’s book: Urantia: The Great Cult Mystery.  However the academic world rather disagrees with Martin Gardner conclusions. 
There is no way to gauge how many adherents there may be as there is no central organization to census. Informal study groups "tend to sprout, ripen, then vanish or splinter" and have not been counted reliably. Readers sometimes join study groups after reading on their own for years or decades, others join them soon after developing an interest in the book, while "for most, worship remains as individual as the act of reading." The movement generally incorporates a non-sectarian view reflective of the values of personal religious experience supporting the contention that individuals with different religious backgrounds can engage the book's teachings as enrichment rather than as a contradiction of their faiths. 
The movement inspired by The Urantia Book has not developed clergy or institutions such as churches, reading rooms, or temples. Sarah Lewis assesses that the movement is uncontroversial compared to other ones, "lacking the zealous proselytizing found within many other groups,” and that it is therefore likely to remain small and unaffected by opposing views. 
Urantia Foundation advocated a "slow growth" policy in the past and has not significantly marketed the book. Sales by Urantia Foundation went from 7,000 in 1990 to 24,700 in 1997, and steadily increased to nearly 38,000 in 2000, an "upturn that seems to represent a genuine trend rather than just some spike on a sales chart.”  Total worldwide sales since 1955 are estimated to have reached 700,000 at the end of 2011. Since initial publication in English the book has been translated it into 14 other languages. Approximately half of the books distributed by Urantia Foundation are in languages other than English, particularly Spanish and Russian. Since the book was determined to be in the public domain in 2001, other organizations, such as The Urantia Book Fellowship under the publishing name Uversa Press, have also published the book. Copies of The Urantia Book are on the Internet in various formats and it has been adapted to more recent platforms such as the Kindle and the iPhone /iPad / iPod Touch. Several audio books of the text are also on the Internet. 
Urantia Association International had twenty-six reader associations worldwide as of 2002, and the Urantia Book Fellowship (formerly Urantia Brotherhood, founded in 1955 as the original social fraternal organization) claimed roughly twelve hundred official members, with the highest concentrations in the West of the United States and the Sun Belt, especially California, Colorado, Florida, and Texas. It appears an increasing number of people are forming study groups, participating in Internet discussion groups, online education, and hosting or visiting websites dedicated to The Urantia Book. Reader conferences take place around the world. 
 Lewis, James R. and Hammer, Olav (2007). The Invention of Sacred Tradition.Cambridge University Press.
 Larry Mullins with Dr. Meredith Justin Sprunger (2000) A History of the Urantia Papers. Penumbra Press
 Urantia Foundation (1955), The Urantia Book,
 Sadler, William S. (1929), The Mind at Mischief: Tricks and Deceptions of the Subconscious and How to Cope with Them, Funk and Wagnalls
 Christopher H. Partridge UFO Religions (2003) Routledge
 Rosemary Ellen Guiley (1991) Encyclopedia of Mystical and Paranormal Experience. Grange Books
 House, Dr. H. Wayne (2000), Charts of Cults, Sects, and Religious Movements, Zondervan
 Larson, Bob (2004), Larson's Book of World Religions and Alternative Spirituality, Tyndale House Publishers, Inc.,
 Gooch, Brad (2002). Godtalk: Travels in Spiritual America. Alfred A. Knopf.
 Gardner Book Review by Library Journal from the Library Journal/April 15, 1995 Book Reviews
 Melton, J. Gordon (1990), New Age Encyclopedia (1st ed.), Gale Research, Inc.
 2011 Urantia Foundation annual report (http://www.urantia.org/news/2012-06/urantia-foundation-annual-report-2011)
 Gardner, Martin (1995), Urantia: The Great Cult Mystery, Prometheus Books