The theme of this book is the life of God. It is about the shared life that God engenders and the God whose very being is a sharing. Christians are used to speaking of the life that God engenders within the Church as ‘communion’, of the Christian life as a participation in the life of God, and of the life that is God as love. There is one Greek word that can be used for all three: koinonia, of which the Latin translation is communio. This book is an exploration of koinonia/communio as the terms have been used in current ecumenical discussion and in the formation of the Christian tradition. There has in recent years been a ground-swell of interest in ‘community’ and in society as a ‘community of communities’. An exploration of what it means for the Church to be that unique human community which is explicitly constituted by its communion in God, Father, Son, and Holy Spirit, is potentially a resource for the renewal of secular social thought, and the insights of secular social thought of the greatest value in renewing our understanding of the common life of the Christian Church.

In much ecumenical literature, the Latinate communion or communio is used interchangeably with the Greek koinonia. These two words do, however, have differing resonances because of their differing provenance: the very different history and understanding of the churches and societies in East and West.