Denmark has a strong foundation in terms of sustainability, making the country an interesting backdrop for studying how the overarching sustainability agenda has shaped education practice. This study investigated the scope and status of sustainability education targeted at grade 4-6 students in Danish out-of-school science education institutions, such as natural history museums, science and technology museums, science centres, zoos and aquaria. First, a desktop review took place to map educational programmes with sustainability content. Second, five representative programmes were selected for further study. Thematic analysis of observation field notes and interviews with educators and teachers yielded four themes that collectively defined the sustainability programmes: institution, formal education, content and pedagogy. The final sections of the paper contextualise these themes, and discuss their implications for sustainability education in out-of-school practice. The study concludes by offering reflections on constructive future pathways for sustainability education.