Including a global context while initiating transdisciplinary education for sustainable development locally, is urgent. In literature review rhetoric still dominates. There is a demand for investigating teacher experiences of transdisciplinary sustainability teaching within a global framework. In particular as the process of learning towards sustainability in global–local settings is often stated as critical. Research on new settings of teaching and learning approaches, with the potential to facilitate real transdisciplinary thinking, and seeking to implement SD into the curriculum, must be given priority. This empirical study of teachers´ understanding of their teaching of Global Learning for Sustainable Development (GLSD) records subsequent educational development steps identifying the challenges. A phenomenographic approach with semi-structured interview questions is used to research teachers’ experiences of extending towards transdisciplinary GLSD teaching. Within a longitudinal study teachers at an upper secondary school reflect on real practices focusing critical aspects experienced. The investigation shows teachers´ understanding of their teaching of GLSD. Continuity in the didactic process of initiating globalisation of teaching ESD is hardly extraordinary. Because of the complexity of SD issues, it is necessary to bring in an open-minded elucidation of the globalization aspects actually at hand in the foundation of the SD concept. Comprehensively examined, a foundation built on knowledge capabilities for transdisciplinary teaching approaches characterized by signs of capability to learn and act globally could be considered forceful and holistic in its nature , instead of relying on a competence-base.