Flanders (Belgium) is one of the most densely populated regions in Europe. Intensive land use, widespread suburbanization, inadequate environmental qualities, and fragmentation everywhere deteriorate living conditions and put pressure on species and natural habitats. In the past, several governmental initiatives were launched to establish a coherent ecological network to improve the situation. Despite the set objectives, only a little progress was made. Therefore, to establish green infrastructure, a new approach that moves away from previous top-down and one-sided strategies is developed. Making use of Green Infrastructure as a boundary concept, interpretation was given through an open and participatory process. The core is the identification of common objectives (ecosystem services or other objectives/services), the selection of appropriate green infrastructure elements to support the services, and the co-design of a network taking the local socio-ecological realm into account. By applying the methodology in concrete urban and rural projects, we learned that establishing strong coalitions of stakeholders, obtaining and sharing reliable knowledge of the systems are key to an effective realization of green infrastructure.