Abstract In this paper we aim to investigate the underlying mechanisms of the maintenance of ISO 14001. Initially, we looked into the Hillary's [Hillary R. Evaluation of study reports on the barriers, opportunities and drivers for small and medium sized enterprises – the adoption of environmental management systems. Report for DTI Envirodoctorate 5th October, 1999. London: NEMA; 1999] evaluation study on barriers, opportunities and drivers for small and medium enterprises that adopted environmental management systems and we developed a comprehensive list of barriers identified in the literature. We have used this set of barriers to investigate the underlying mechanisms in the maintenance of ISO 14001 environmental management system through an in-depth longitudinal case study in manufacturing organisations. We have determined five underlying processes (transforming and value adding; administrating and improving; understanding and accepting; communicating and learning; availability of resources) and five key actors (external environment; environmental management team; ISO 14001 EMS; organisation; resources and skills), which interactions are captured in M-ISO model. Finally, based on our study we offer directions for future research.