Interdisciplinary inquiry presupposes an open worldview to enable the researcher to transcend the confinements of a specific discipline in order to become aware of aspects that are necessary to satisfyingly solve a problem. Radical constructivism offers a way of engineering such interdisciplinarity that goes beyond mere multi or pluridisciplinary approaches. In this paper I describe epistemological and methodological aspects of interdisciplinarity, discuss typical problems it faces, and carve out its relationship with knowledge and communication from a constructivist perspective. Five implications for interdisciplinary practice and science education conclude the paper.