Unlike geothermal power generation, in which heat energy is converted to electricity, direct-use applications use heat energy directly to accomplish a broad range of purposes. The temperature range of these applications is between ~10°C and ~150°C. Given the ubiquity of this temperature range in the shallow subsurface, these types of applications of geothermal energy have the potential to be installed almost anywhere that has sufcient uid available. In this chapter, the basic principles that underlay these applications will be detailed and examples of the applications will be discussed. We will begin the discussion by examining the estimates of the magnitude of the resource.