The EGS concept is to extract heat by creating a subsurface fracture system in rocks into which water can be added through injection wells. Creating an enhanced requires improving the natural permeability of rock. Rocks are permeable due to minute fractures and pore spaces between mineral grains. Injected water is heated by contact with the rock and returns to the surface through production wells, as in naturally occurring hydrothermal systems. EGS are reservoirs created to improve the economics of resources without adequate water and/or permeability. EGS offer great potential for dramatically expanding the use of geothermal energy.