In the petroleum industry, well logging is a well developed discipline that has matured over a fifty-year period. Compared to this, geothermal well logging is a very new field of activity. The current practice is to use the same logging equipment and the same log interpretation techniques for geothermal wells as had been used for petroleum wells. However, this approach has proven either inadequate or ineffective in most geothermal areas. The problems here are of two types: (1) those associated with logging equipment and operation, and (2) those connected with log interpretation techniques. This paper focuses on the log interpretation aspects only. 6 refs