The study of Mission and Migration has developed rapidly in recent years. This article aims to scope the field by examining a variety of trajectories from different disciplines and by suggesting ways in which enquiries may be furthered. It examines contemporary missiological thought, insights from the New Testament and comprehensions of diaspora, of belonging and of pilgrimage, providing diverse examples. It suggests pursuing a spirituality of radical hospitality and a methodology that widens the term of sociological enquiry. The focus of this wide-ranging collection of interlocking themes is provided by the exploration of common witness in Christ. The reflections on identity and on academic enquiry indicate why multi-ethnic witness to Christ, in a globalised era of mass migration, proves difficult to achieve. It uses the “is” provided by social science as a springboard for the “ought” of biblical and missiological vision.