A look at history showed that theology always has to face contemporary demands in terms of its scientific character. At present, processes of pluralisation and secularisation challenge the existence of theology at universities not only against the background of religious studies, which are independent of the churches, but also, for example, in relation to innovative life sciences or cognitive sciences. In this context, an essential point to consider was that theology – like social systems in general and science in particular – is characterised by an increasing differentiation. This differentiation of science implied an increasing specialisation of research, which could also be observed in the field of theology and its sub-disciplines. This article accordingly addressed the question of how, in the face of increasingly specialised research studies, the unity of theology can be justified beyond abstract and sweeping determinations. The present contribution suggested that in this respect a model of research designs developed in religious didactics might prove useful. This model of research design could essentially be understood as consisting of three research dimensions (topics, reference theories and methodologies) that define a research space, in which the research study on the didactics of religion can be located in the three-dimensional space by the research goal as a formatting factor. The three dimensions of this model (topics, reference theories and methodologies), including the research goal, seemed to be broad enough to be tested in other sub-disciplines of theology as well to see whether their research can be more closely defined with them.Contribution: Accordingly, the contribution of this article was to raise the question, in view of an increasing specialisation of theological research, to what extent a model of research designs developed in the didactics of religion could be transferred to other sub-disciplines of theology. Should this succeed a new approach to justifying the unity of theology could become available, which is able to take into account the current differentiation of theology.