Purpose: Many higher education institutions are committed to developing students as skilled professionals and responsible citizens for a more sustainable future. In addition to the formal curriculum for sustainability education, there is an increasing interest in informal learning within universities. This paper aims to extend the current understanding of the diversity and significance of informal learning experiences in supporting students' learning for sustainability. Design/methodology/approach: Six focus groups were formed with 30 undergraduate and postgraduate students from an Australian higher education institution committed to supporting graduate competencies for sustainability. An inductive and qualitative inquiry was designed to enable participants to reflect on the ways in which their university experiences support meaningful and significant learning for sustainability. Findings: The paper presents a typology of the diverse communities of informal learning that students create and engage with. These range from ongoing to transient groups, from environmentally to more socially oriented groups and from incidental to intended learning, from local to national in scale, with varying types and degrees of connection to the formal curriculum and the university campus. The paper demonstrates that these student-led experiences support three domains of learning: cognitive, practical and affective. Originality/value: Deepening the understanding of the forms and significance of student-led learning within their university experience contributes to the identification of the roles that informal learning may play alongside formal education in developing graduates as agents of change for a more sustainable future.