["Environmental Policy and Governance, EarlyView. ", "\nABSTRACT\nOpen space networks provide multiple ecosystem services and other benefits which are particularly important to urban regions. Accordingly, there are many examples around the world of urban‐regional open space policies such as regional parks and green belts that connect non‐built‐up areas over several municipalities. Yet it is still unclear how and why this kind of policy can prevail in regional political decision‐making against often strongly competing forms of land use. In this conceptual paper, we elaborate a theoretical approach to explain the adoption and implementation of the mentioned open space policies. Focusing on policy‐making and planning processes, we use the well‐established Multiple Streams Framework (MSF), originally developed by Kingdon, which has been subsequently refined and extended over the years. Drawing on relevant strands of literature, our paper applies the MSF to the field of open space policy‐making and planning in conurbations. In line with our understanding of the framework, the likelihood of a significant policy being adopted and implemented in this policy field increases when three largely independent process streams (problem, policy and political) are coupled by a capable policy entrepreneur during a policy window, and this coupling is subsequently maintained. Our approach goes beyond Kingdon's original MSF by introducing an initial and an implementation phase to the analysis. At the same time, we integrate many process‐related aspects of spatial and open space research into our MSF‐based theoretical approach. The result is summarised in a set of seven propositions.\n"]