In this special issue titled ‘Sustainability and SMEs: Opening the black box’, we compile eight articles that dissect the multifaceted relationship between small- and medium-sized enterprises (SMEs) and sustainability. This special issue promoted interdisciplinary research at the intersection of the design, management, organisation, and reporting of sustainable actions in the context of SMEs. Stemming from the need to apply different theoretical and analytical lenses to the study of sustainability in SMEs than in large corporations, each paper provides unique insights into the formal and informal approaches, drivers, barriers, and enablers of sustainable practices in SMEs. The collection not only furthers the dialogue on the role of SMEs in sustainable development but also paves the way for future research directions and practical applications in this dynamic and still underexplored field.