The appearance of new sciences and conflicts arising from reductionism in domain of science and knowledge, explains the necessity of interdisciplinary studies. Some scientists believe the history of interdisciplinary studies is rooted in ancient Greece, but in fact interdisciplinary studies started in industrial laboratories, the first center for interdisciplinary studies, about 150 years ago. Like every phenomenon interdisciplinary studies base on some foundations. What kind of sorts do they have? How these foundations explain this approach? This article proposes three foundations; logical base, epistemological base and cognitive base. The methodological pluralism is the most important logical base for interdisciplinary studies. Integration is the most important epistemological base in this approach. Finally complicated systems and their formulas are the most important cognitive base in Interdisciplinary approach. This article tries to explain interdisciplinary studies by these bases and then tries to explain traits of these bases. It also surveys some offshoot problems such as definitions of interdisciplinary approach, kinds of it and its expansion in all of fields. The interdisciplinary approach is multiple origins. The multiple origin problems are rooted in various sciences and they cannot be survey by single science. The study of religion and professional ethics are samples of multiple origin disciplines. Interdisciplinary studies are necessary for humanities because of its complex subject, that is, human. So it cannot study by single science.
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