The Sociology of Religious Movements.

He taught short courses in the sociology of religious movements at the Athenaeum Pontificium Regina Apostolorum and in 2005-2006 at the Pontifical University of the Holy Cross, both Vatican-accredited institutions.

In his book The Sociology of Religious Movements (1996), William Sims Bainbridge cites the research of Roy Wallis, in noting "Scientology ... has no discernible connection to Christianity".

In 2012 he joined the faculty of the Pontifical Salesian University, also accredited by the Vatican, as a professor of Sociology of Religious Movements and, as of 2013, of Sociology of Religions.