Christian theology is necessarily a human, intellectual endeavour which listens. It believes that God has spoken decisively in Christ, and that God's Word is yet able to be heard in every generation. Listening, therefore, is a primary virtue in theology. But Christian theology and ethics must also listen to the understanding diligently provided by other, more secular, intellectual endeavours. The word of revelation may be heard there too. Only when theology performs the double act of listening to the voices of its traditions, and the voices surrounding those traditions, is it able to make connections between Christian faith and ordinary life, and perhaps to indicate humbly how the gospel of Christ may be capable of touching and transforming it. Perhaps there is no ethical problem where this double act is as apt as in the case of cohabitation. People in many parts of the world now live together before marriage, after marriage, and instead of marriage, in numbers which have been increasing remarkably for the last thirty years. Sociologists, ethnologists and demographers have made valiant attempts to track, chart and perhaps explain this unprecedented shift in family formation. The results are available for theologians (and everyone else) to study and deploy. The whole of the present chapter is an attempt to listen to secular authors as they describe and explain cohabitation.