Oneirology is the study of dreams. In the second century A.D., a Greek named Artemidorus wrote a book called Oneirocritica. It was one of the earliest dream books ever written. It means "The Interpretation of Dreams." In 1900, in honor of this ancient book, Sigmund Freud wrote his own dream book called "The Interpretation of Dreams." The study of dreams and the use of dreams in the life of an individual and a culture is probably older than written history. Certainly, for "primitive" or "indigenous" peoples, including our own Native Americans, dreams were central to the daily life of the individual and the tribe.
In such cultures dreams were used by the individual for physical healing, for help in determining their livelihood, determine who they were going to marry, and receive important information about their children. For the tribe as a whole, important things like where to hunt, information about their enemies, and when and where to move the tribe were never considered without the input of tribal dreams. Every important decision, whether personal or tribal, was determined from dreams.
The history of dreams, from biblical times to the present, is filled with the important ways in which dreams have been used by individuals and cultures. This includes the Torah, with Daniel and Joseph as dream interpreters. It includes the New Testament with Joseph being warned in a dream to escape with the baby Jesus to save his life. Dreams have played an important part in politics, art, science, invention, and religion, just to name a few. Lincoln dreamed about his own death before it happened. Caesar's wife Calpurnia was warned in a dream that he should not go to the senate. Important scientific breakthroughs and inventions have come out of the dream state.
One could write a whole book about the history and uses of dreams and someone has. I direct you to Robert Van De Castle's "Our Dreaming Mind." It is a wonderful compendium of the history and benefits of dreaming.