This article is written from within the Catholic, and more particularly the Augustinian/Thomist tradition of moral theology. It analyses the response of the Catholic Magisterium to the prospect of germline-genetic engineering (GGE). This is a very new issue and the Church has little definitive teaching on it. The statements of Popes and Vatican congregations or commissions have not settled the key questions. An analysis of theological themes drawn from secular writers points beyond pragmatic safety considerations toward intrinsic ethical limits to GGE. Given the impossibility of identifying would-have-been-created persons who would be “treated” by this intervention, altering the human genome for the sake of future generations cannot be regarded as “therapy.” Further theological considerations suggest that GGE may not be morally permissible, even in the case of identifiable genetic diseases. This is an area where more theological reflection is needed.