Occupational science, stemmed from occupational therapy, is a new basic social science defined as the systematic study of the human as an occupational being. Mary Reilly argued that occupational therapy profession should reorganize its academic structure of knowledge by embracing traditional emphasis on occupation. Supporting Reilly’s view, Elizabeth J. Yerxa and her colleagues developed a doctoral program in occupational science with suggestions that the basic science (occupational science) of occupation should focus on the explanation of occupation, whereas the applied science (occupational therapy) should emphasize advancing knowledge on the use of occupation in treatment. The priority of occupational science is to promote theories about the form, function, and meaning as well as the sociocultural context of occupation so that the profession of occupational therapy can be nourished. The major contribution of occupational science to occupational therapy will be providing a body of knowledge sharply focused on the concept of occupation which will help in justification and enhancement of occupational therapy practice.