There are many advantages to geothermal energy. Geothermal energy is renewable energy because once water or steam is used it can be pumped back into the ground. It is also clean energy. Geothermal power plants, unlike plants that burn fossil fuels, do not produce greenhouse gases that can be harmful to the atmosphere.Geothermal energy is energy available as heat contained in or discharged from the earth's crust that can be used for generating electricity and providing direct heat for numerous applications such as: space and district heating; water heating; aquaculture; horticulture; and industrial processes. In addition, the use of energy extracted from the constant temperatures of the earth at shallow depth by means of ground source heat pumps (GSHP) is also generally referred to as geothermal energy.In this regard, present book have been prepared in 3 chapters that chapter 1 gives an introduction to geothermal energy and its applications. Chapter Two deals design of rural heating System in Iran, and Chapter 3 deals with data analysis.