All natural language processing systems (such as parsers, generators, taggers) need to have access to a lexicon about the words in the language. This thesis presents a lexicon architecture for natural language processing in Turkish. Given a query form consisting of a surface form and other features acting as restrictions, the lexicon produces feature structures containing morphosyntactic, syntactic, and semantic information for all possible interpretations of the surface form satisfying those restrictions. The lexicon is based on contemporary approaches like feature-based representation, inheritance, and unification. It makes use of two information sources: a morphological processor and a lexical database containing all the open and closed-class words of Turkish. The system has been implemented in SICStus Prolog as a standalone module for use in natural language processing applications.