Knowledge management deals with explicit knowledge and tacit (or implicit) knowledge. One form of tacit knowledge is an individual?s mental model-a hypothetical knowledge structure that integrates the ideas, assumptions, relationships, insights, facts, and misconceptions that together shape the way an individual views and interacts with reality. The purpose of this paper is to explore these mental models, why they need to be made explicit, and how such externalization can be accomplished. Specifically, after a review of the mental model theory, we propose a new technique for determining an individual?s mental model based on his/her decisions in several selected situations within a specific decision domain.