Comparisons need a tertium comparationis. Traditionally this is sought on neutral terrain in order to arrange the comparison in a manner that is as unprejudiced as possible. But comparisons cannot avoid following specific interests and perspectives. They cannot be made with entirely neutral and objective categories. The tertium comparationis is never neutral territory, but rather ground gained from the side of one of the views entering into the comparison - and from there always in danger of being merely a projective abstraction. Since neutrality and objectivity are thus unattainable in cross-religious and cross-cultural contexts, Comparative Theology has to be conceived as dialogical or collaborative and interactive theology. At least in the research practice favored by me, it strives to form mixed, religion-connecting research groups in which the people concerned always have their say and are included dialogically in their own research. Comparative standards and criteria are thus themselves brought into the respective research and negotiation processes. At this point, theology has the advantage over religious studies that it must already reflect on where its respective concepts, categories, and epistemological interests reside within the framework of a contingent, fallible tradition of knowledge. This is part of the very self-understanding of the discipline, and thus it cannot so easily fall victim to projective abstraction. The paper wants to describe how theology can be reconceived as comparative theology and tries to develop some case studies to explain how comparisons can work in such a dialogical and collaborative framework. These examples will be taken from Muslim-Christian contexts and they will try to show how this framework can help to reshape the role of law within Catholic theology. It will try to explore how comparative law can be developed within comparative theology.