Purpose: Inter- and transdisciplinarity are core concepts in almost all education for sustainable development (ESD) competence frameworks and curricula. To equip students with inter- and transdisciplinary competencies is highly demanding for educators. Educators must not only know how to teach students such competencies, but need to be experienced in inter- and transdisciplinary research and must have some technical knowledge about inter- and transdisciplinarity. This paper aims to show how university educators can be supported in their teaching. Design/methodology/approach: The paper is a case study based on research and on experiences in interdisciplinary teaching and in supporting educators in their interdisciplinary teaching. Findings: The paper presents a competence framework of interdisciplinary competencies to guide university teachers that has been developed, implemented and refined in interdisciplinary study programmes belonging to the field of ESD. It shows how the professional development of educators could be addressed referring to the experiences in these programmes. The measures presented consist for one thing of interdisciplinary processes among the educators and of measures directly supporting educators in their teaching for another thing. Originality/value: The case study the paper refers to is of special value, first, because the experiences are based on long-standing research and on two decades of experiences. Second, because considerable efforts were made to deliver coherent and consistent interdisciplinary teaching in which interdisciplinarity was not only a teaching subject for the students but showed by the educators as well so that the educators involved did not only talk about competencies for inter- and transdisciplinary collaborations but also set an example in their own doings.