Comparative theology is a growing field within Christian theology and there are analogues to it in other theological traditions as well. As such, it is indebted to multiple sources and belongs to none exclusively. But in its currently form it is notably and richly rooted in the Roman Catholic tradition which, despite its limitations, has always balanced being-Catholic with a wider catholicity, ever finding a home for the faith in new languages and cultures. Catholic engagement with other religions proceeds with confidence in rationality, in adherence to the principle of the presence of God in all things, and by way of a sacramental imagination and skill in intuitive rapprochement, even when engaging traditions which, at first glance, are very different from the Catholic. This grounded catholicity serves as roots for comparative theology, not just at the beginnings of Catholic interreligious encounters, but as a key dimension of its current interreligious engagements. The great innovators of the missionary era after 1500 CE are famed for their energetic engagement with cultures across the world, an engagement that manifested Catholic adaptive practices operative since the beginnings of Christianity. In the twentieth century and particularly after Vatican II, Catholic engagement with other religions has been marked even more vigorously by a disposition toward inclusion, the affirmation of whatever is good and holy in other traditions, attention to the particular and, despite prudent doctrinal hesitations, a willingness to experiment and discover incrementally the meeting points among traditions. Such dispositions, old and now new, form a particular and distinctive lineage for today’s comparative theology.