Filioque
Elizabeth Teresa Groppe.  Yves Congar's Theology of the Holy Spirit. New York: Oxford University Press, 2004. See esp. pp. 75–79, for a summary of Congar's work on the Filioque. Congar is widely considered the most important Roman Catholic ecclesiologist of the twentieth century. He was influential in the composition of several Vatican II documents. Most important of all, he was instrumental in the association in the West of pneumatology and ecclesiology, a new development.