Joachim Wach is most important for having conceived of a study of religions as a discipline, independent of theology and the philosophy of religion on the one hand and of the social sciences on the other. Wach was born and worked in Germany until 1935, when the Nazis expelled him because of his Jewish ancestry. (He was descended from the great Jewish philosopher Moses Mendelssohn and his son Felix Mendelssohn [see Vol. 3], the composer, who converted to Christianity). From 1935 until his death, Wach taught in the United States, first at Brown University, than at the University of Chicago. Wach envisioned the study of religion in terms of a model of experience, expression, and understanding. In his view, religious phenomena are expressions of religious experience in three specific areas of life---the theoretical, the practical, and the sociological. The aim of the study of religions is to understand the meanings of these expressions. Wach's work during the German period laid the philosophical foundations for this endeavor. He identified two fundamental components in an independent study of religions: historical study and systematics, in other words, a comparative study of general religious forms and patterns. His American works pay particular attention to the systematic study of the sociological dimension of religion, making particular use of the typological method often associated with Max Weber.