Gerhard Albert Baum OC (June 20, 1923 – October 18, 2017), better known as Gregory Baum, was a German-born Canadian priest and theologian in the Roman Catholic Church. He became known in North America and Europe in the 1960s for his work on ecumenism, interfaith dialogue, and the relationship between the Catholic Church and Jews. In the later 1960s, he went to the New School for Social Theory in New York and became a sociologist, which led to his work on creating a dialogue between classical sociology (Marx, Tocqueville, Durkheim, Toennies, Weber, etc.) and Christian theology.