The aim of INSULAE is to foster the deployment of innovative solutions for the EU islands decarbonization by developing and demonstrating at three Lighthouse Islands (located in Croatia, in Denmark and in Portugal) a set of interventions linked to seven replicable use cases, whose results will validate an Investment Planning Tool that will be then demonstrated at four Follower Islands (located in Spain, in Germany, in The Netherlands Antilles and in Greece) for the development of four associated Action Plans. The chosen islands are complementary in many aspects: location, size, connection with the mainland, economic development, renewable share and carbon intensity. INSULAE contributes to the Clean Energy for EU Islands Initiative by providing an Investment Planning Tool (IPT) able to create Actions Plans for the islands to generate their own sustainable, low-cost energy. The interventions will prove the ability of the use cases to develop RES-based systems 40-70% cheaper than diesel generation, thus, enabling an average reduction of the fossil fuel consumption of 11% after a large deployment of the use cases in the INSULAE islands. The INSULAE IPT will support the decision maker on the selection and design of cost effective Action Plans looking for the island decarbonization. It will be mainly composed by two modules: the Island modeling assistant and the Scenarisation module. The project team is carefully balanced along all the value chain counting with five public authorities, six energy and water utilities, four technology providers, two energy software developers, six RTOs, one environment NGO, one business models expert, one engineering company and one entity for social aspects and replication. The legal and regulatory framework of 57% of the total population living in EU islands will be directly considered within the project.