The concept of sustainable development in recent decades has aroused the interest of many experts and researchers in various scientific fields at international and national diversity. However, sustainable development remains recognized as a topic that needs further research, especially in the field of education (adults) for sustainable development. The theoretical part of this paper provides a summary of the approach to defining sustainable development and a presentation of the main principles and goals of sustainable development with special emphasis on quality education in the context of education (adults) for sustainable development and the role and competencies of teachers in education (adults) for sustainable development in the context of sustainable development in teaching. The empirical part of the paper presents the results of a research conducted on a sample of teachers in adult education employed in adult education institutions in the Republic of Croatia. The results show that the teachers who participated in the research show mostly positive attitudes towards the concepts of sustainable development and education for sustainable development, however less knowledge about these concepts, especially about the concept of education for sustainable development. The results show that, although they consider sustainable development topics important for adult education and teach some of them, less than half of teachers consider it necessary (additionally) to implement them in the subject they teach. On average, teachers estimate that they largely possess almost all generic (general) and specific competencies, but only partially those that are directly related to the implementation of sustainable development in teaching in adult education. The results of the research show that teachers are ready and motivated to learn and improve in the field of education for sustainable development, but only partially feel ready to implement sustainable development in teaching.