Seas and oceans have been for centuries places where people, goods and cultures move and are exchanged. During the last few decades, various human activities have increasingly crowded these places, requiring special attention on how to manage their interaction/conflicts and their impact on the environment. Maritime Spatial Planning (MSP) is a key example where requests coming from multiple sectors -e.g. energy, fisheries, hazard mitigation, transportation, tourism, conservation - need to be balanced to address sometimes contrasting overall objectives like Blue Growth and Ecosystem Based Management. Taking a “good” decision in such a complex and continuously evolving context is definitely a challenge and requires the involvement of multiple economic actors, domain experts and political stakeholders. The process includes the collection and elaboration of huge amount of data, the use of spatially-aware tools, the active participation of stakeholders and the preparation of a set of alternative and/or complementary scenarios to be presented and explained to decision makers. Understanding how plans are built, which data are behind maps, who contributed to the definition of objectives and priorities, what questions addressed alternative scenarios, are all fundamental elements for taking “good” decisions. During last years, important steps have been made in the definition and testing of procedural and practical steps to address those issues, both in the scientific and research community and from the implementation point of view. During the next few years, all EU Member States are required to establish spatial plans for their marine waters; understanding how they are going to be implemented is a key issue that needs to be supported by adequate skills and competences not only for the people who will build the plan, but also (or even more) for the decision makers who will take decisions based on those plans.