The Filioque controversy refers to the theological dispute over the phrase 'and the Son' in the Nicene Creed, which concerns the procession of the Holy Spirit from both the Father and the Son. This disagreement emerged between the Western Church, which included the papacy, and the Eastern Orthodox Church led by the patriarchs, contributing to significant tensions that played a role in the schism between these two branches of Christianity. The implications of this debate extended beyond theology, influencing political and cultural relations, especially during the time of the Crusades.