The thesis presents the hypothesis that the systematic theology of Paul Tillich (1886-1965) offers significant new benefits towards church unity. The methodology used in pursuit of this aim, is a critical analysis of Tillich's early and late thought. Tillich' s work was influenced by the German philosophical and theological schools and came to expression in American academia in his publication Systematic Theology. The results of this analysis reveal Tillich's consistent commitment to the concept of Gestalt. This finding has been broadened to include the concept that the strength of ecclesial unity is dependent upon the understanding that every ecclesial denomination is an effective element in the constituency of the whole Church. This argument is supported by a deconstruction of Tillich' s system that is keyed into the hermeneutical theories of Gadamer and Derrida. The system is then reconstructed in terms of a new Gestalt that turns on the hypothesis that there is a relationship of synthesis between philosophy and theology within the Tillichian system, rather than the complementary relationship that Tillich claims. This conclusion is based upon the system being perceived as being founded upon the Western classical philosophical and theological traditions. A critique of Tillich's incorporation of modern existential hermeneutics into this system is made principally in relation to the existentialist thought of Kierkegaard, Heidegger and Sartre. A hermeneutic of Tillich' s existential critique serves to highlight the questions that result from existential disruption rather than to label him as an existentialist per se. The system is thus moved forward into the post-modern context under new hermeneutics. An analysis of Tillich's ecclesiology reveals that this is both eschatological and Trinitarian in nature. The relationship between Tillich's system and ecclesiology is brought into dialogue by means of their being expressed in terms of an ecclesiological circle. These hermeneutics are compared and contrasted with the ecclesiologies of Zizioulas and Haight and the published ecumenical documents of The World Council of Churches in order to reveal their commonalties. When the system has thus been applied to the current ecumenical dialogue, then it becomes apparent that the raison d'etre of Tillich's system is the Church and the raison d'etre of the Church is the system. The squaring of Paul Tillich's ecclesiological circle is thus made complete.