Comparative public law is a meeting place for a number of different research traditions: doctrinally oriented comparative public law, the qualitative tradition in socio-legal studies, and the comparative dimension of American political science research on public law. While almost everyone agrees that a transnational, multidisciplinary conception of the field is therefore necessary, exactly how these different traditions should relate to each other has not been satisfactorily resolved. Existing suggestions amount either to disguised colonisation of one research tradition by another or unhelpful bromides about the benefits of interdisciplinary dialogue. After explaining the different epistemologies and methods underpinning each of comparative public law’s constituent research traditions, this paper proposes a critical engagement model for cross-disciplinary interaction in the field. According to this model, the integrity of each distinct tradition needs to be respected. Doctrinally oriented comparative law research, for example, cannot be reduced to supplying concepts for positive political science theory-building. It has its own distinct epistemology and methods. Starting from this position of mutual respect, all researchers in the field should consult research emanating from other traditions for two main purposes: as a source of potentially useful findings and as a corrective on the tendency of their own tradition to develop blind spots. In certain circumstances, carefully designed interdisciplinary research projects should also be possible.