This paper summarizes the results of a recent study (the Facilities Improvement Report) performed with funding by the Public Interest Energy Research (PIER) program of the California Energy Commission (CEC). The Facilities Improvement Report describes potential improvements to 45 existing power plants in 7 currently producing geothermal fields in California. The improvements are of two general types: improvements in resource supply and improvements in surface facilities. To resolve inconsistencies in reported plant capacities, distinctions are made between original capacity, electromechanical capacity, 2005 capacity (which takes into account resource limitations), and actual annual average power. The total electro-mechanical capacity of the geothermal plants in California is about 2,650 MW-gross, and the 2005 capacity is about 1,850 MW-gross (1,600 MW-net).