ENEL carried out demonstration activities at Fusina Power Plant (PP), aimed at proving the feasibility of RDF (Refuse Derived Fuel)/coal co-firing. Since 2004, RDF has been co-fired with coal on two 320 MWe boilers (Units 3 and 4). Since February 2009 the average RDF share has been increased up to 5% on thermal input for each Unit at full load. In the period 2008-2012, Fusina PP was involved in the European Founded DEBCO (Demonstration of Biomass Co-combustion) Project, focused on the demonstration of large scale biomass co-firing and supply chain integration. In this framework, a series of activities were carried out at the PP, including the long term monitoring of RDF quality and boiler performance, the assessment of the Air Pollution Control Devices (APCDs) as well as the evaluation of possible uses of the ash residues. The impact of RDF co-firing on the boiler performance was evaluated in terms of combustion efficiency, thermal losses, corrosion (monitored in the long term by means of probes both on the boiler walls and at the convective pass), slagging and fouling. The experimental activities included the leading of Joint Measurement Campaigns (JMCs) as well as laboratory analyses. In the present paper, the main findings of the aforesaid activities are described, starting from the RDF quality monitoring and moving all through the phases of the co-firing process: milling, burning, flue gas treatment, ash quality evaluation.