This article explores the relevance of sustainability in international social education (ISE). Our empirical data is based on a survey of 30 social work students from Switzerland, Austria, Germany and Sweden. Theoretically, we draw on Bronfenbrenner's theory of social ecosystems and Dewey's emphasis on democratic learning. We use a qualitative approach based on Strauss' Grounded Theory, which allows us to dig deep into the meanings of the students we interviewed. The interviewed students experienced more or less continuously that learning in an international context is learning with all senses, is a "24/7 learning", and is learning in another language (at least most of the time). The results of our survey underline that acquiring knowledge in an international context contributes to a comprehensive understanding of social work as a profession and to the formation of a broad and professional identity. This includes a broad range of critical and systemic thinking skills that enable enquiry, integration and holistic thinking, i.e. sustainability.