Renewable energy resources (RES) have exceptional importance in the principles of sustainable development and energy management. Using the practically unlimited internal heat of the Earth, geothermal energy has one of the highest potentials among all renewables to meet these principles and related challenges. It should be pointed out that Central and Eastern European countries also have geothermal resources suitable for a wide range of applications, including a significant heating sector. However, to date they have either remained unexploited due to several reasons or their use has been carried out in an unsustainable manner; in some cases geothermal district heating projects lack the energy efficiency and sustainability components when, as often is the case, spent water is not reinjected back into the reservoirs but is instead released to surface waters. The EU–supported project “Geothermal communities – demonstrating the cascaded use of geothermal energy for district heating with small scale RES integration and retrofitting measures”, GEOCOM, carried out in 2010–2015 (www.geothermalcommunities.eu) was an initiative to promote the wider use of geothermal energy in sustainable and innovative ways. The key activities and issues covered by the GEOCOM project were as follows: o Pilot scale demonstration works on geothermal energy applications for heating in three different municipalities: Galanta (Slovakia), Montieri (Italy), and M.rahalom (Hungary). Geothermal uses were integrated with some other RES in order to outline ways of more efficient and more sustainable energy production. In some cases an additional focus was the trapping of methane from ground water for energy production. For all pilot installations the energy efficiency measures were applied by thermal retrofitting and optimisation. An efficient monitoring system was applied to the demonstration activities; o Technological research on the integration, optimisation and applications of energy systems, to help the demonstration activities of the project become more efficient; o Socio– economic research on the public perception and understanding of geothermal energy, other renewables and measures promoting the rational use of energy to ease the preparation of similar future projects; o Transboundary issues on the exploitation of geothermal energy (based on the example of the geothermal reservoirs situated within the territories of Hungary and Serbia); o Pro-active training and dissemination activities; o Initiating and facilitating the networking of interested communities in the GEOCOM and other European countries by setting up the Mayors Geothermal Club. The direct objective of the GEOCOM project was to demonstrate succesful, innovative and inspiring examples of the utilisation of geothermal energy for heat generation employing cutting-edge, environmentally sustainable and cost competitive technologies combined with innovative energy efficiency measures, integration with other renewable energy sources and retrofitting at three different pilot– sites (municipalities) listed above. These pilot scale geothermal energy applications are given as examples of good practices in this Handbook. All three cases present intermediary phases between ongoing investments and planned future projects that will take into account the lessons learned from the pilot phases. The key results achieved thanks to the GEOCOM works in pilot sites are highlighted below. ; FP7