The greatest challenge to ecumenical dialogue has come not from discussions on justification by faith or papal primacy or even infallibility, but from discussions related to the Virgin Mary. This remarkable assertion is the reason behind noted theologian and ecumenist George Tavard's historical and ecumenical investigation of the image of Mary. 

Mary belongs not only to Christians but to Jews and Muslims as well. In a broad sense she can also be seen in relation to female symbols of the Absolute not as divinity but as divine. Time and changes in dogma have also affected the way Mary is perceived. Tavard has therefore divided his investigation into five parts. He gathers insights from Scripture (Part I), Tradition (Part II), the Reformation (Part III), the Modern Age (Part IV), and World Religions (Part V). Together these perspectives clarify and enhance the Theotokos and her ties with the people of God. George H. Tavard, a member of the Augustinians of the Assumption, professor emeritus of theology at the Methodist Theological School in Ohio, and distinguished professor of theology at Marquette University, was a peritus at Vatican Council II, where he was involved in preparing the decree on ecumenism. He has participated in several international and American ecumenical dialogues and has written extensively on theology and ecumenism.