This study presents the developments in the theology of the topic of primacy and unity of the Christian churches in the last century and a half, primarily among Greek Orthodox and Roman Catholic theologians. Issues treated range from claims of papal primacy to whether other analogous forms of primacy of a bishop in a church may be historically warranted and ecclesiologically sound, or whether the notion itself is to be rejected as incompatible with the catholicity of each local church. The leitmotiv is the thought of John Zizioulas, the prominent Greek ecumenical theologian, in the context of other Greek and Russian Orthodox authors. In this doctoral dissertation written in English, Vgenopoulos makes a persuasive case for the focus on the nuanced affirmation of primacy as understood by Zizioulas.

Primacy, on this view, whether in a local church headed by a bishop, or in regional or autocephalous groups of churches, or in the church universal, implies a real responsibility and influence of the primate within the framework of synodality. It does not, however, include a power of jurisdiction as normally understood. This latter was of course reaffirmed for the Roman Catholic Church at Vatican II, along with a new or renewed emphasis on an ecclesiology of communion. In this timely work one has a careful summary of how ecumenical thought has arrived at this point.