This special issue contains 13 papers describing the concept, historical background, development and current status of the Soultz EGS (Enhanced Geothermal System) project in France. The impacts of this project on the geological environment, water-rock interactions on fracture permeability, and on seismic velocity are discussed. Also covered are the use of numerical code in studying the impact of fluid density on the pressure distribution and stimulation volume in Soultz, tracer testing of the geothermal heat exchanger, and modelling of coupling between free and forced convection in a vertical permeable slot. Finally, the application of HDRec (Hot Dry Rock economic) software for the cost-benefit analysis of geothermal projects is also discussed.