Protestant theologian and one of the foremost scholars in the modern study of religion.

As a professor of the history of religion at the University of Leipzig (1929–35) and the University of Chicago (Chicago, University of) (1945–55), Wach contributed significantly to the field of study that became known as the sociology of religion. He is credited with introducing into American scholarship the phenomenological method of analyzing religious beliefs and practices. He established the discipline known as the comparative study of religion (Religionswissenschaft) at the University of Chicago and is considered the founder of the so-called Chicago School, from which emerged such influential scholars as Mircea Eliade.

Wach conceived Religionswissenschaft as a comparative, phenomenological, and psychological approach to religion, including the theoretical (or mental; i.e., religious ideas), the practical (or behavioral), and the institutional (social) aspects of religion. Because of his concern with the study of religious experience, he was also interested in the sociology of religion, attempting to indicate how religious values shaped the institutions that expressed them. Among Wach's writings in English are Sociology of Religion (1944), Types of Religious Experience—Christian and Non-Christian (1951), and The Comparative Study of Religions (1958).