This paper describes the implementation and system details of Klex, a finite-state transducer lexicon for the Korean language, developed using XRCE’s Xerox Finite State Tool (XFST). Klex is essentially a transducer network representing the lexicon of the Korean language with the lexical string on the upper side and the inflected surface string on the lower side. Two major applications for Klex are morphological analysis and generation: given a well-formed inflected lower string, a languageindependent algorithm derives the upper lexical string from the network and vice versa. Klex was written to conform to the part-of-speech tagging standards of the Korean Treebank Project, and is currently operating as the morphological analysis engine for the project.