The purpose of this paper is to present an application of fuzzy logic as an organizational framework for a knowledge-based interpretation system in the domain of geotechnical engineering. Knowledge-based systems (KBS) are emerging as a powerful means of dealing with the ill-structured problems encountered in many engineering and medical applications1. (It has been stated2 that expert systems are problem-solving programs that solve substantial problems generally conceded as being difficult and requiring expertise. They are called knowledge-based because their performance depends critically on the use of facts and heuristics (or rules of thumb) used by experts). In a KBS, the knowledge or rules of judgement pertaining to the domain are encoded in the system in an explicit manner; these rules can be examined and modified, if necessary. This is in contrast to the way traditional algorithmic programs are structured. The motivation for this project was two-fold: generally, to demonstrate that knowledge-based techniques are powerful problem-solving tools that can be applied to task areas within geotechnical engineering; and specifically, to develop a KBS to interpret geotechnical characterization data from cone penetrometers.