Except for some excellent studies on the notion of koinonia, few works have been devoted to a revival of the entire vision of the Church around communion, a vision of ecclesiology which is rooted in the solidarity that finds its locus in Jesus Christ. Church of Churches, the fruit of several years of research, teaching, and ecumenical involvement, is intended to overcome this lack. It is not an exhaustive study but rather a point of departure for discussing how the vision of the ecclesiology of communion - the most difficult question of the ecumenical debate - can break down the barrier of misunderstanding, suspicions, and claims in which the diverse ecclesial traditions are locked.