In the framework of the achievement of the EU Climate and Energy packages for the decarbonisation of the energy sectors, the integration of variable renewable energy sources will put at stake the stability and provision security of the electricity system: there is a growing need for flexibility provision to ensure a reliable and stable electric system. MAGNITUDE addresses the challenge to rise flexibility in electricity systems, by increasing the synergies between electricity, heating/cooling and gas networks and associated systems. MAGNITUDE will bring technical solutions, market design and business models, to be integrated on ongoing policy discussions. MAGNITUDE will define technological and operational means for maximising flexibility provision to the electricity network. It will identify the regulatory framework to bring such flexibility service to the energy markets and will provide enhanced market designs and related business mechanisms. MAGNITUDE is built upon 7 real life case studies of multi energy systems, located in different European countries, under different regulatory and geopolitical environments and with different technological development levels. It will: 1. Simulate the multi energy systems in the case studies and optimise their operation strategies maximising the provision of specific flexibility services 2. From existing regulations, propose improved market designs, and integrate them in a market simulation platform for evaluating its performance among the case study countries 3. Quantify the benefit of pooling flexibilities from decentralized multi energy systems for energy markets through an aggregation platform. MAGNITUDE results will define policy strategies and recommendations in a pan-European perspective. Achievements will be spread among stakeholders to raise awareness and foster higher collaboration among the electricity, heating and gas sectors to achieve the common goal of a less carbon intensive, yet reliable energy system.