Geologic investigations span a broad range of topics and scales. Geologic mapping, lithologic studies of drill core and cuttings, evaluation of mineral distributions, interpretation of satellite images, fluid-inclusion investigations and the structural analysis of faults and fractures are among the various studies frequently incorporated into geothermal exploration and development programs. Taken together, the results of these investigations provide the basis for the conceptual models used to site production and injection wells. As the initial geothermal targets progress from the prospect stage to a fully developed field these models are continually updated and refined. At EGI, the heart of its geologic investigations is the Geothermal Sample Library, which houses drill samples from geothermal systems throughout the world.