To support sustainable development, several researchers in ergonomics propose a comprehensive approach to work situations or the systems in which they are embedded. This article empirically instantiates one of the proposed models – the Sustainable System of Systems (SSoS) model – in the case of the work of farmers engaged in agroecological transitions. It thus explores complexity regarding sustainability, and to highlight its contributions and limits. Based on a case study, our results illustrate how the macro, meso and micro levels of SSoS are finely articulated in workers’ concerns, decisions, and trajectories to sustainability. We enrich this approach with a diachronic method to support the actors involved in such transitions as they navigate the complexities of sustainable transition.