Sustainability education, or Education for Sustainable Development (ESD) as it is often referred to in policy discussions, is an educational approach based on the idea that education should contribute to a sustainable world. Whereas conventional scholastic education typically emphasises the learning of content in the form of predefined knowledge or skills, ESD aims to encourage students to act in more sustainable ways. This shift of aim raises a question: should ESD be addressed primarily within general or subject-specific education? It is most commonly addressed in general education because of the competence-based approach of ESD, and it is this issue that forms the subject of this chapter. Based on Biesta’s suggestions about the main purposes of education and Young’s work on the idea of powerful knowledge and possible curriculum trajectories for the future, this chapter argues that there is a need to adopt a multidisciplinary perspective in ESD that relies on contributions from multiple subject-specific teaching traditions. Moreover, findings from empirical studies are used to show how a transformative language education strategy can play a major role in empowering students’ action competence for sustainability.