Education for Sustainable Development (ESD) has become a central priority in global education, aiming to empower learners to make responsible decisions and take meaningful action across environmental, social, and economic dimensions (UNESCO, 2020). Integrating ESD into English language teaching (ELT) offers opportunities to develop sustainability awareness alongside linguistic and critical thinking skills. Although previous studies highlight the important role of language educators in promoting sustainability (Bowden, 2010; Bedir, 2021; Arslan & Curle, 2024), little is known about how EFL teachers working in higher education conceptualize and implement ESD, despite universities' well-recognized potential to advance sustainability agendas. This qualitative case study investigates how EFL teachers at state universities in Türkiye understand sustainability and ESD, perceive institutional responsibilities, and integrate sustainability themes into their teaching. Semi-structured interviews were conducted with eight instructors, and the data were analysed through inductive content analysis. Findings show substantial variation in teachers’ conceptualizations, ranging from environmentally focused understandings to broader, SDG-aligned interpretations. Most participants assigned higher education institutions a central role in supporting ESD through curriculum alignment, resource provision, and professional development, yet institutional practices were often perceived as limited or symbolic. ESD integration in the classroom was largely incidental, commonly emerging through coursebook topics or spontaneous discussions rather than systematic pedagogical planning. Teachers also identified several challenges—including insufficient institutional support, lack of training, the sensitivity of some ESD themes, student disengagement, and curriculum/time constraints—alongside enabling factors such as personal interest, student relevance, technological tools, and the presence of sustainability-related content in existing materials. The study concludes that while ESD has strong potential to enrich ELT by fostering critical, reflective, and globally aware learners, meaningful implementation requires stronger institutional commitment, enhanced teacher preparation, and curriculum redesign. Recommendations include embedding ESD in teacher education programs, increasing institutional support, and promoting student-centered sustainability initiatives within higher education.