IANOS brings together two Lighthouse (LH) islands (Terceira-PT, Ameland-NL), and three Fellow islands (FI) (Lambedusa-IT, Bora-Bora-FR, Nisyros-GR), all sharing a common vision of decarbonizing their energy systems and be energy independent until 2050. Thirty-four (33) strongly experienced partners from nine (9) European countries, join forces to deliver smart technological, economic and social innovations, providing systemic optimization starting from an Energy Community-centric approach. IANOS adopts an Island Energy Transition Strategy built around three (3) Island Energy Transition Tracks that focus on: a) Energy efficiency and grid support for extremely high RES penetration, b) Decarbonization through electrification and support from non-emitting fuels, c) Empowering Local Energy Communities (LEC). Through IANOS an impressive repository of elements (technologies, tools, methods) will be demonstrated in the two LH islands and within nine (8) carefully defined Use-Cases (UCs) that will lead to: a reduction of fossil fuel consumption by 326.4 GWh/y, an increase in RES utilization by 26.5 GWh/y, increase accuracy of vRES forecasts by >10% and reduce energy bills of end-users by >15%. In total, 900 participants (prosumers/consumers) will be involved in LECs by the end of IANOS. Elements to be demonstrated include: an iVPP operative orchestration toolkit, smart energy routers, hybrid transformers, flywheel storage, biobased batteries, heat batteries, tidal kite, and the IANOS Energy Planning and Transition Suite (IEPT). The replication potential of IANOS UCs will be evaluated in the three FIs. Due to their current local energy mix, Terceira and Ameland can particularly act as LHs for geothermal and hydrogen-centered island economies, respectively. To reach all these goals, a total of 121.6M€ will be invested by the 2 LH ecosystems, while another 60.4M€ will be fuelled by the 6 FI ecosystems during IANOS (until 2025).