In this analysis two Danish case studies are investigated using a spatial planning approach. The first case study concerns the area on the west coast of Denmark that has been elected as test site by the Danish Wave Energy Center (DanWEC), a foundation constituted by local authorities, Aalborg University supported by the national wave energy industry. The second case study attains the Danish portion of the western Baltic sea, where many offshore windfarms are already installed and many projects are in construction or in the planning stage. The environmental background for the two areas is considered through set of multiple indicators (e.g. sea bottom topography and characteristics, marine biodiversity, presence of vulnerable species). Environmental indicators are aggregated into environmental impact indexes that constitute the basis for evaluating the site suitability for Marine Renewable Energy Installations (MREIs). Concurrently, areas of potential conflicts between the interests of MREI developers and commercial, recreational users are identified. Multivariate analysis techniques allow to disentangle the different components of the environmental vulnerability of the two areas and suggest sound criteria for the optimal siting of these infrastructures. The two case studies, concerning respectively a regional and local scale, offer good examples about how spatial planning has the potential to guide the transition from the single sector management toward the integrated management of sea uses.