Gregory Baum was a Canadian priest and theologian in the Roman Catholic Church. He emigrated to Canada from England as a war refugee with his Jewish mother and Protestant father. In the 1960s, he was known for his works on ecumenism, interfaith dialogue, and the relationship between the Catholic Church and Jewish populations. Later in the decade, he attended the New York School for Social Theory and became a sociologist, specializing in social ethics and the sociology of religion. As a theological advisor, he composed the first draft of the conciliar document Nostra aetate, the Declaration on the Relation of the Church with Non-Christian Religions, that was later expanded to address all the world religions. A final draft was promulgated by the pope in 1965. Baum taught theology and sociology at the University of Saint Michael’s College in the University of Toronto, before moving to McGill in 1986. In the late 1980s, he moved back to Quebec and developed an interest in Quebec Catholicism, which he saw as more progressive and contextual than its English Canadian and American counterparts. He was the author of numerous works, including The Credibility of the Church Today (1968), Religion and Alienation (1977), and Compassion and Solidarity: The Church for Others (1988, which was based on his 1987 CBC Massey Lectures). In 1990, he was made an Officer of the Order of Canada. He died in 2017.