This article focuses on the coordination of long-term social-ecological monitoring programmes between different organisations. Effective long-term social-ecological monitoring (LTSEM) is considered to be of crucial importance to inform conservation policies in an era of accelerating global changes. However, many LTSEM programmes are led by individual organisations with a narrow thematic and spatial focus, and fail to provide an integrated understanding of the trajectories of social-ecological systems. Inter-organisational coordination is increasingly presented as a promising way to overcome this limitation of LTSEM programmes, but in practice it remains limited. Our article contributes to understanding this situation by empirically documenting how inter-organisational coordination of LTSEM programmes is organised and enacted in practice. It proposes a working heuristic framework to characterise patterns of interorganisational coordination based on two criteria: the degree of monitoring centrality and the degree of verticality of inter-organisational coordination. This framework can be used to compare patterns of inter-organisational coordination both across cases and over time. The article also proposes recommendations for the coordination of LTSEM programmes led by different organisations, especially in the early stages of the coordination process. enabling activities and horizontal relationships. In the LOP, no organisation felt threatened by 252 the project as long as eLTER permitted some leeway in the selection of variables to be 253 monitored. This facilitated monitoring-centred activities and a more vertical pattern of 254 coordination. Our study therefore suggests that horizontal relationships and monitoring-255 enabling activities are better suited to the early stages of coordination between highly 256 heterogeneous organisations with little shared history, low trust and significant power 257 asymmetries. Vertical relationships and/or monitoring-centred activities, in contrast, can be 258 envisaged from the outset when coordinating similar organisations with a long shared history, 259 high trust and limited power asymmetries. 260 5. Conclusions 261 Effective LTSEM is crucial for informing conservation policies and depends especially on the 262 capacity to achieve inter-organisational coordination. We explored how inter-organisational 263 coordination in LTSEM is organised and enacted in practice by comparing two contrasting 264 cases from a French organisation committed to the long-term study of mountain SESs. Based 265 on this empirical study, we have developed a working heuristic framework that allows 266 patterns of inter-organisational coordination to be analysed and compared both across cases 267 and over time. Our framework is based on two criteria: the degree of monitoring centrality 268 and the degree of verticality of inter-organisational coordination. Further empirical studies are 269 needed to refine it; to test its ability to account for a variety of cases of coordination; and to 10.