Purpose: The educational community -- particularly higher education -- should contribute to the new generation's understanding of what sustainability entails. To do this, teachers must be aware of the need for education for sustainability. However, little is known about how university teachers understand or represent sustainability. This study aims to bridge the gap identified in the literature concerning university teachers' representation of sustainability. Design/methodology/approach: A total of 403 teachers from the University of the Basque Country participated in the study through a free association exercise based on the grid elaboration method. Findings: In general terms, teachers are aware of the three dimensions that constitute sustainability, but differences were found in the way sustainability was represented depending on several factors such as the teaching field, previous knowledge of the 2030 Agenda and gender. Despite awareness of the need to incorporate sustainability, there was also reticence toward the way in which sustainability is being addressed in higher education. Those results were discussed considering the previous literature on sustainability. Practical implications: The results allow the authors to conclude that knowledge of the 2030 Agenda leads teachers to have a more complete representation and greater recognition of sustainability. Thus, it would be necessary for universities to offer more training to teachers to promote a holistic understanding of sustainability and facilitate its incorporation into teaching. Originality/value: The use of this method made it possible to collect, in a less biased and much more direct way, the teachers' voices, to know the type of representation (holistic) or partial (only one of its dimensions: environmental, economic or social) that they have of sustainability, and to check whether their representation was linked to specific factors.