Introduction: Not only in early human societies, even today, there are people who tried to interpret dream spiritually. According to different functions of sleep and dreaming in human daily life, dream and sleep are of interest in modern science. Evolution of scientific study of dreaming during the history of medicine as well as current theories of dream have discussed in this manuscript. On the other hand, due to connection of sleep and dreaming, sleep physiology and pathology have shortly described. Conclusion: Despite of significant improvement in dream study and different theories to explain dream and sleep functions, further studies are needed to integrate all aspect of dream and sleep in human.