Non-formal education for promoting sustainability has become popular over the last decade. In 2017, the International Review of Education journal dedicated a special issue to non-formal and community learning for sustainable development. This study makes a case for“ non-formal adult education” (NFAE) to also be included in the discussion. It aims to reveal current themes of the research literature related to education for sustainable development (ESD) in the context of NFAE, by analyzing research articles published in 15 peer-reviewed journals during the years 2015-2020. Two main questions structured this study: How is research on sustainability approached by researchers in NFAE? What are the current research themes of NFAE for sustainability? The analysis identified three different approaches of conducting research on promoting sustainability in the field of adult education: place and community-based learning approach, transformative learning approach, and ecological and environmental literacy approach. The study also revealed two research themes of NFAE for promoting sustainability and further identified the research gaps. Accordingly, eco-justice, barriers to sustainability, and social inequalities might be prominent areas of research.