Geothermal technologies use the clean, sustainable heat from the Earth. Geothermal resources include the heat retained in shallow ground, hot water and rock found a few miles beneath the Earth's surface, and extremely high-temperature molten rock located deep in the Earth.

For a technology overview try:

DOE Geothermal Technologies Website:
http://www.eere.energy.gov/basics/renewable_energy/geothermal.html

Geothermal Energy Association - http://geo-energy.org/Basics.aspx

For geothermal industry news try:

Think Geothermal - http://thinkgeoenergy.com/news